diff --git a/packages/kysely-driver/tsconfig.json b/packages/kysely-driver/tsconfig.json
index 44dd2dfd..c902b0ed 100644
--- a/packages/kysely-driver/tsconfig.json
+++ b/packages/kysely-driver/tsconfig.json
@@ -5,11 +5,7 @@
     "declaration": true /* Generates corresponding '.d.ts' file. */,
     "esModuleInterop": true /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */,
     "forceConsistentCasingInFileNames": true /* Disallow inconsistently-cased references to the same file. */,
-    "lib": [
-      "DOM",
-      "ES2020",
-      "WebWorker"
-    ] /* Specify library files to be included in the compilation. */,
+    "lib": ["DOM", "ES2020", "WebWorker"] /* Specify library files to be included in the compilation. */,
     "module": "es2020" /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */,
     "moduleResolution": "node" /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */,
     "outDir": "./lib" /* Redirect output structure to the directory. */,
@@ -18,7 +14,10 @@
     "strict": true /* Enable all strict type-checking options. */,
     "target": "es6" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
   },
-  "include": [
-    "src/**/*",
+  "include": ["src/**/*"],
+  "references": [
+    {
+      "path": "../powersync-sdk-common"
+    }
   ]
 }
diff --git a/packages/powersync-sdk-common/src/client/AbstractPowerSyncDatabase.ts b/packages/powersync-sdk-common/src/client/AbstractPowerSyncDatabase.ts
index 849fcd11..b1ac652c 100644
--- a/packages/powersync-sdk-common/src/client/AbstractPowerSyncDatabase.ts
+++ b/packages/powersync-sdk-common/src/client/AbstractPowerSyncDatabase.ts
@@ -114,7 +114,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
     super();
     this.bucketStorageAdapter = this.generateBucketStorageAdapter();
     this.closed = true;
-    this.currentStatus = null;
+    this.currentStatus = undefined;
     this.options = { ...DEFAULT_POWERSYNC_DB_OPTIONS, ...options };
     this._schema = options.schema;
     this.ready = false;
@@ -201,7 +201,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
     try {
       schema.validate();
     } catch (ex) {
-      this.options.logger.warn('Schema validation failed. Unexpected behaviour could occur', ex);
+      this.options.logger?.warn('Schema validation failed. Unexpected behaviour could occur', ex);
     }
     this._schema = schema;
     await this.database.execute('SELECT powersync_replace_schema(?)', [JSON.stringify(this.schema.toJSON())]);
@@ -291,7 +291,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
         [tableGlob]
       );
 
-      if (!existingTableRows.rows.length) {
+      if (!existingTableRows.rows?.length) {
         return;
       }
       for (const row of existingTableRows.rows._array) {
@@ -325,11 +325,11 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
           `SELECT SUM(cast(data as blob) + 20) as size, count(*) as count FROM ${PSInternalTable.CRUD}`
         );
 
-        const row = result.rows.item(0);
+        const row = result.rows!.item(0);
         return new UploadQueueStats(row?.count ?? 0, row?.size ?? 0);
       } else {
         const result = await tx.execute(`SELECT count(*) as count FROM ${PSInternalTable.CRUD}`);
-        const row = result.rows.item(0);
+        const row = result.rows!.item(0);
         return new UploadQueueStats(row?.count ?? 0);
       }
     });
@@ -388,7 +388,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
    * Unlike {@link getCrudBatch}, this only returns data from a single transaction at a time.
    * All data for the transaction is loaded into memory.
    */
-  async getNextCrudTransaction(): Promise<CrudTransaction> {
+  async getNextCrudTransaction(): Promise<CrudTransaction | null> {
     return await this.readTransaction(async (tx) => {
       const first = await tx.getOptional<CrudEntryJSON>(
         `SELECT id, tx_id, data FROM ${PSInternalTable.CRUD} ORDER BY id ASC LIMIT 1`
@@ -543,7 +543,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
 
     const resolvedTables = options?.tables ?? [];
     if (!options?.tables) {
-      const explained = await this.getAll(`EXPLAIN ${sql}`, parameters);
+      const explained = await this.getAll<{ opcode: string; p3: number; p2: number }>(`EXPLAIN ${sql}`, parameters);
       const rootPages = _.chain(explained)
         .filter((row) => row['opcode'] == 'OpenRead' && row['p3'] == 0 && _.isNumber(row['p2']))
         .map((row) => row['p2'])
@@ -571,10 +571,11 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
    * Note, do not declare this as `async *onChange` as it will not work in React Native
    */
   onChange(options?: SQLWatchOptions): AsyncIterable<WatchOnChangeEvent> {
-    const watchedTables = options.tables ?? [];
+    const resolvedOptions = options ?? {};
+    const watchedTables = resolvedOptions.tables ?? [];
 
     let throttledTableUpdates: string[] = [];
-    const throttleMs = options.throttleMs ?? DEFAULT_WATCH_THROTTLE_MS;
+    const throttleMs = resolvedOptions.throttleMs ?? DEFAULT_WATCH_THROTTLE_MS;
 
     return new EventIterator<WatchOnChangeEvent>((eventOptions) => {
       const flushTableUpdates = _.throttle(
@@ -593,7 +594,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
 
       const dispose = this.database.registerListener({
         tablesUpdated: async (update) => {
-          const { rawTableNames } = options;
+          const { rawTableNames } = resolvedOptions;
 
           const tables = isBatchedUpdateNotification(update) ? update.tables : [update.table];
 
@@ -613,7 +614,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
         }
       });
 
-      options.signal?.addEventListener('abort', () => {
+      resolvedOptions.signal?.addEventListener('abort', () => {
         dispose();
         eventOptions.stop();
         // Maybe fail?
@@ -626,7 +627,7 @@ export abstract class AbstractPowerSyncDatabase extends BaseObserver<PowerSyncDB
   /**
    * @ignore
    */
-  private async executeReadOnly(sql: string, params: any[]) {
+  private async executeReadOnly(sql: string, params?: any[]) {
     await this.waitForReady();
     return this.database.readLock((tx) => tx.execute(sql, params));
   }
diff --git a/packages/powersync-sdk-common/src/client/AbstractPowerSyncOpenFactory.ts b/packages/powersync-sdk-common/src/client/AbstractPowerSyncOpenFactory.ts
index 2273605e..0e7135db 100644
--- a/packages/powersync-sdk-common/src/client/AbstractPowerSyncOpenFactory.ts
+++ b/packages/powersync-sdk-common/src/client/AbstractPowerSyncOpenFactory.ts
@@ -33,7 +33,6 @@ export abstract class AbstractPowerSyncDatabaseOpenFactory {
   generateOptions(): PowerSyncDatabaseOptions {
     return {
       database: this.openDB(),
-      schema: this.schema,
       ...this.options
     };
   }
diff --git a/packages/powersync-sdk-common/src/client/sync/bucket/CrudEntry.ts b/packages/powersync-sdk-common/src/client/sync/bucket/CrudEntry.ts
index 3f8efdc2..64ef48ea 100644
--- a/packages/powersync-sdk-common/src/client/sync/bucket/CrudEntry.ts
+++ b/packages/powersync-sdk-common/src/client/sync/bucket/CrudEntry.ts
@@ -33,7 +33,7 @@ export type CrudEntryDataJSON = {
 };
 
 /**
- * The output JSOn seems to be a third type of JSON, not the same as the input JSON.
+ * The output JSON seems to be a third type of JSON, not the same as the input JSON.
  */
 export type CrudEntryOutputJSON = {
   op_id: number;
@@ -41,7 +41,7 @@ export type CrudEntryOutputJSON = {
   type: string;
   id: string;
   tx_id?: number;
-  data: Record<string, any>;
+  data?: Record<string, any>;
 };
 
 /**
diff --git a/packages/powersync-sdk-common/src/client/sync/bucket/SyncDataBucket.ts b/packages/powersync-sdk-common/src/client/sync/bucket/SyncDataBucket.ts
index 5f6a9c7b..06e5b9fb 100644
--- a/packages/powersync-sdk-common/src/client/sync/bucket/SyncDataBucket.ts
+++ b/packages/powersync-sdk-common/src/client/sync/bucket/SyncDataBucket.ts
@@ -16,7 +16,7 @@ export class SyncDataBucket {
     return new SyncDataBucket(
       row.bucket,
       row.data.map((entry) => OplogEntry.fromRow(entry)),
-      row.has_more,
+      row.has_more ?? false,
       row.after,
       row.next_after
     );
diff --git a/packages/powersync-sdk-common/src/client/sync/stream/AbstractStreamingSyncImplementation.ts b/packages/powersync-sdk-common/src/client/sync/stream/AbstractStreamingSyncImplementation.ts
index b5edd2bd..61afabb7 100644
--- a/packages/powersync-sdk-common/src/client/sync/stream/AbstractStreamingSyncImplementation.ts
+++ b/packages/powersync-sdk-common/src/client/sync/stream/AbstractStreamingSyncImplementation.ts
@@ -46,7 +46,7 @@ export interface AbstractStreamingSyncImplementationOptions {
 }
 
 export interface StreamingSyncImplementationListener extends BaseListener {
-  statusChanged?: (status: SyncStatus) => void;
+  statusChanged?: ((status: SyncStatus) => void) | undefined;
 }
 
 export const DEFAULT_CRUD_UPLOAD_THROTTLE_MS = 1000;
@@ -69,7 +69,7 @@ export abstract class AbstractStreamingSyncImplementation extends BaseObserver<S
     this.options = { ...DEFAULT_STREAMING_SYNC_OPTIONS, ...options };
     this.syncStatus = new SyncStatus({
       connected: false,
-      lastSyncedAt: null,
+      lastSyncedAt: undefined,
       dataFlow: {
         uploading: false,
         downloading: false
@@ -245,7 +245,7 @@ export abstract class AbstractStreamingSyncImplementation extends BaseObserver<S
             await this.options.adapter.setTargetCheckpoint(targetCheckpoint);
           } else if (isStreamingSyncCheckpointComplete(line)) {
             this.logger.debug('Checkpoint complete', targetCheckpoint);
-            const result = await this.options.adapter.syncLocalDatabase(targetCheckpoint);
+            const result = await this.options.adapter.syncLocalDatabase(targetCheckpoint!);
             if (!result.checkpointValid) {
               // This means checksums failed. Start again with a new checkpoint.
               // TODO: better back-off
@@ -325,7 +325,7 @@ export abstract class AbstractStreamingSyncImplementation extends BaseObserver<S
                 lastSyncedAt: new Date()
               });
             } else if (_.isEqual(validatedCheckpoint, targetCheckpoint)) {
-              const result = await this.options.adapter.syncLocalDatabase(targetCheckpoint);
+              const result = await this.options.adapter.syncLocalDatabase(targetCheckpoint!);
               if (!result.checkpointValid) {
                 // This means checksums failed. Start again with a new checkpoint.
                 // TODO: better back-off
@@ -355,7 +355,7 @@ export abstract class AbstractStreamingSyncImplementation extends BaseObserver<S
     });
   }
 
-  async *streamingSyncRequest(req: StreamingSyncRequest, signal: AbortSignal): AsyncGenerator<StreamingSyncLine> {
+  async *streamingSyncRequest(req: StreamingSyncRequest, signal?: AbortSignal): AsyncGenerator<StreamingSyncLine> {
     const body = await this.options.remote.postStreaming('/sync/stream', req, {}, signal);
     const stream = ndjsonStream(body);
     const reader = stream.getReader();
diff --git a/packages/powersync-sdk-common/src/db/crud/SyncStatus.ts b/packages/powersync-sdk-common/src/db/crud/SyncStatus.ts
index 49047503..f81d91b2 100644
--- a/packages/powersync-sdk-common/src/db/crud/SyncStatus.ts
+++ b/packages/powersync-sdk-common/src/db/crud/SyncStatus.ts
@@ -53,7 +53,7 @@ export class SyncStatus {
   }
 
   getMessage() {
-    const { dataFlow } = this.options;
+    const dataFlow = this.dataFlowStatus;
     return `SyncStatus<connected: ${this.connected} lastSyncedAt: ${this.lastSyncedAt}. Downloading: ${dataFlow.downloading}. Uploading: ${dataFlow.uploading}`;
   }
 }
diff --git a/packages/powersync-sdk-common/src/db/crud/UploadQueueStatus.ts b/packages/powersync-sdk-common/src/db/crud/UploadQueueStatus.ts
index 53fcde73..b440f039 100644
--- a/packages/powersync-sdk-common/src/db/crud/UploadQueueStatus.ts
+++ b/packages/powersync-sdk-common/src/db/crud/UploadQueueStatus.ts
@@ -7,7 +7,7 @@ export class UploadQueueStats {
     /**
      * Size of the upload queue in bytes.
      */
-    public size: number = null
+    public size: number | null = null
   ) {}
 
   toString() {
diff --git a/packages/powersync-sdk-common/src/db/schema/Index.ts b/packages/powersync-sdk-common/src/db/schema/Index.ts
index 2f68c64d..c7b1f0d4 100644
--- a/packages/powersync-sdk-common/src/db/schema/Index.ts
+++ b/packages/powersync-sdk-common/src/db/schema/Index.ts
@@ -27,7 +27,7 @@ export class Index {
   }
 
   get columns() {
-    return this.options.columns;
+    return this.options.columns ?? [];
   }
 
   toJSON(table: Table) {
diff --git a/packages/powersync-sdk-common/src/db/schema/Table.ts b/packages/powersync-sdk-common/src/db/schema/Table.ts
index 2543337e..3f10d174 100644
--- a/packages/powersync-sdk-common/src/db/schema/Table.ts
+++ b/packages/powersync-sdk-common/src/db/schema/Table.ts
@@ -54,7 +54,7 @@ export class Table {
   }
 
   get viewName() {
-    return this.viewNameOverride || this.name;
+    return this.viewNameOverride ?? this.name;
   }
 
   get columns() {
@@ -62,15 +62,15 @@ export class Table {
   }
 
   get indexes() {
-    return this.options.indexes;
+    return this.options.indexes ?? [];
   }
 
   get localOnly() {
-    return this.options.localOnly;
+    return this.options.localOnly ?? false;
   }
 
   get insertOnly() {
-    return this.options.insertOnly;
+    return this.options.insertOnly ?? false;
   }
 
   get internalName() {
diff --git a/packages/powersync-sdk-common/src/utils/BaseObserver.ts b/packages/powersync-sdk-common/src/utils/BaseObserver.ts
index 2cfd89d6..6881c8c1 100644
--- a/packages/powersync-sdk-common/src/utils/BaseObserver.ts
+++ b/packages/powersync-sdk-common/src/utils/BaseObserver.ts
@@ -5,7 +5,7 @@ export interface BaseObserverInterface<T extends BaseListener> {
 }
 
 export type BaseListener = {
-  [key: string]: (...event: any) => any;
+  [key: string]: ((...event: any) => any) | undefined;
 };
 
 export class BaseObserver<T extends BaseListener = BaseListener> implements BaseObserverInterface<T> {
diff --git a/packages/powersync-sdk-common/src/utils/mutex.ts b/packages/powersync-sdk-common/src/utils/mutex.ts
index 57b7226e..d1a06064 100644
--- a/packages/powersync-sdk-common/src/utils/mutex.ts
+++ b/packages/powersync-sdk-common/src/utils/mutex.ts
@@ -16,10 +16,12 @@ export async function mutexRunExclusive<T>(
           timedOut = true;
           reject(new Error('Timeout waiting for lock'));
         }, timeout)
-      : null;
+      : undefined;
 
     mutex.runExclusive(async () => {
-      clearTimeout(timeoutId);
+      if (timeoutId) {
+        clearTimeout(timeoutId);
+      }
       if (timedOut) return;
 
       try {
diff --git a/packages/powersync-sdk-common/tsconfig.json b/packages/powersync-sdk-common/tsconfig.json
index fa91ee71..3f9b79e0 100644
--- a/packages/powersync-sdk-common/tsconfig.json
+++ b/packages/powersync-sdk-common/tsconfig.json
@@ -18,7 +18,8 @@
     "noStrictGenericChecks": false,
     "resolveJsonModule": true,
     "skipLibCheck": true,
-    "target": "esnext"
+    "target": "esnext",
+    "strictNullChecks": true
   },
   "include": ["src/**/*"]
 }
diff --git a/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeRemote.ts b/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeRemote.ts
index 1aeb626e..34b03e2a 100644
--- a/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeRemote.ts
+++ b/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeRemote.ts
@@ -90,7 +90,9 @@ export class ReactNativeRemote extends AbstractRemote {
       throw ex;
     });
 
-    clearTimeout(timeout);
+    if (timeout != null) {
+      clearTimeout(timeout);
+    }
 
     if (!res.ok) {
       const text = await res.text();
@@ -108,7 +110,7 @@ export class ReactNativeRemote extends AbstractRemote {
      * The common SDK is a bit oblivious to `ReadableStream` classes.
      * This should be improved when moving to Websockets
      */
-    const reader = res.body.getReader();
+    const reader = res.body!.getReader();
     const outputStream = new ReadableStream({
       start(controller) {
         return processStream();
diff --git a/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeStreamingSyncImplementation.ts b/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeStreamingSyncImplementation.ts
index 55eafaae..caa60d28 100644
--- a/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeStreamingSyncImplementation.ts
+++ b/packages/powersync-sdk-react-native/src/sync/stream/ReactNativeStreamingSyncImplementation.ts
@@ -26,7 +26,7 @@ export class ReactNativeStreamingSyncImplementation extends AbstractStreamingSyn
   initLocks() {
     const { identifier } = this.options;
     if (identifier && LOCKS.has(identifier)) {
-      this.locks = LOCKS.get(identifier);
+      this.locks = LOCKS.get(identifier)!;
       return;
     }
 
@@ -46,7 +46,7 @@ export class ReactNativeStreamingSyncImplementation extends AbstractStreamingSyn
     }
     return lock.acquire(lockOptions.type, async () => {
       if (lockOptions.signal?.aborted) {
-        return null;
+        throw new Error('Aborted');
       }
 
       return lockOptions.callback();
diff --git a/packages/powersync-sdk-react-native/tsconfig.json b/packages/powersync-sdk-react-native/tsconfig.json
index 098a75f4..f9151e9f 100644
--- a/packages/powersync-sdk-react-native/tsconfig.json
+++ b/packages/powersync-sdk-react-native/tsconfig.json
@@ -16,7 +16,8 @@
     "noStrictGenericChecks": false,
     "resolveJsonModule": true,
     "skipLibCheck": true,
-    "target": "esnext"
+    "target": "esnext",
+    "strictNullChecks": true
   },
   "references": [
     {
diff --git a/packages/powersync-sdk-web/tsconfig.json b/packages/powersync-sdk-web/tsconfig.json
index 09f01794..40e6c558 100644
--- a/packages/powersync-sdk-web/tsconfig.json
+++ b/packages/powersync-sdk-web/tsconfig.json
@@ -15,7 +15,8 @@
     "skipLibCheck": true /* Skip type checking of declaration files. */,
     "sourceMap": true /* Generates corresponding '.map' file. */,
     "strict": true /* Enable all strict type-checking options. */,
-    "target": "es6" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
+    "target": "es6" /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */,
+    "strictNullChecks": true
   },
   "include": ["src/**/*", "tests/**/*"]
 }