diff --git a/src/quartz/parser/qasm_parser.cpp b/src/quartz/parser/qasm_parser.cpp
index 41ec7d8a..202c031e 100644
--- a/src/quartz/parser/qasm_parser.cpp
+++ b/src/quartz/parser/qasm_parser.cpp
@@ -144,16 +144,26 @@ bool ParamParser::parse_array_decl(std::stringstream &ss) {
   getline(ss, name);
   name = strip(name);
 
-  // Ensures that the name is unique.
-  if (symb_params_.count(name) > 0) {
-    std::cerr << "Each param must have a unique name: " << name << std::endl;
-    assert(false);
-    return false;
-  }
+  // Determines whether the parameter is being declared or reused.
+  if (first_file_) {
+    // Ensures that the name is unique.
+    if (symb_params_.count(name) > 0) {
+      std::cerr << "Each param must have a unique name: " << name << std::endl;
+      assert(false);
+      return false;
+    }
 
-  // Allocates a symbolic parameter for each element of the array.
-  for (int i = 0; i < len; ++i) {
-    symb_params_[name][i] = ctx_->get_new_param_id();
+    // Allocates a symbolic parameter for each element of the array.
+    for (int i = 0; i < len; ++i) {
+      symb_params_[name][i] = ctx_->get_new_param_id();
+    }
+  } else {
+    // Check that the parameter is declared and of the correct size.
+    if (symb_params_[name].size() != len) {
+      std::cerr << "Parameter size misalignment: " << name << std::endl;
+      assert(false);
+      return false;
+    }
   }
   return true;
 }
diff --git a/src/quartz/parser/qasm_parser.h b/src/quartz/parser/qasm_parser.h
index ee413e73..1216646a 100644
--- a/src/quartz/parser/qasm_parser.h
+++ b/src/quartz/parser/qasm_parser.h
@@ -40,8 +40,8 @@ std::string strip(const std::string &input);
  */
 class ParamParser {
  public:
-  ParamParser(Context *ctx, bool symbolic_pi)
-      : ctx_(ctx), symbolic_pi_(symbolic_pi) {}
+  ParamParser(Context *ctx)
+      : ctx_(ctx), symbolic_pi_(false), first_file_(true) {}
 
   /**
    * Adds an angle array declaration to the registry of symbolic parameters.
@@ -68,6 +68,21 @@ class ParamParser {
    */
   int parse_expr(std::stringstream &token);
 
+  /**
+   * Calling this function allows for symbolic pi values to be enabled or
+   * disabled. When symbolic pi values are enabled, each constant pi/n will be
+   * replaced by the symbolic expression pi(n).
+   * @param v if true, then symbolic pi values will be enabled.
+   */
+  void use_symbolic_pi(bool v) { symbolic_pi_ = v; }
+
+  /**
+   * Calling this function indicates that a file has been entirely parsed. In
+   * particular, after the first file is parsed, only the names and indices of
+   * existing symbolic variables may be used.
+   */
+  void end_file() { first_file_ = false; }
+
  private:
   /**
    * Implementation details for parse_expr when the expression is a constant
@@ -119,6 +134,14 @@ class ParamParser {
    * is evaluated and stored as a floating-point constant.
    */
   bool symbolic_pi_;
+
+  /**
+   * If true, then this parameter parser has already parsed an OpenQASM 3 file.
+   * When parsing the first file, it is expected that all parameter variables
+   * are new. When parsing subsequent files, it is expected that all parameter
+   * variables were defined in the original file.
+   */
+  bool first_file_;
 };
 
 /**
@@ -200,7 +223,7 @@ class QubitParser {
 // Parser from OpenQASM files to CircuitSeq objects.
 class QASMParser {
  public:
-  QASMParser(Context *ctx) : ctx_(ctx), symbolic_pi_(false) {}
+  QASMParser(Context *ctx) : ctx_(ctx), param_parser_(ctx) {}
 
   template <class _CharT, class _Traits>
   bool load_qasm_stream(std::basic_istream<_CharT, _Traits> &qasm_stream,
@@ -223,11 +246,11 @@ class QASMParser {
     return res;
   }
 
-  void use_symbolic_pi(bool v) { symbolic_pi_ = v; }
+  void use_symbolic_pi(bool v) { param_parser_.use_symbolic_pi(v); }
 
  private:
   Context *ctx_;
-  bool symbolic_pi_;
+  ParamParser param_parser_;
 };
 
 // We cannot put this template function implementation in a .cpp file.
@@ -236,7 +259,6 @@ bool QASMParser::load_qasm_stream(
     std::basic_istream<_CharT, _Traits> &qasm_stream, CircuitSeq *&seq) {
   // Results and sub-parsers.
   seq = nullptr;
-  ParamParser param_parser(ctx_, symbolic_pi_);
   QubitParser qubit_parser;
 
   // Generalized control data.
@@ -321,7 +343,7 @@ bool QASMParser::load_qasm_stream(
       }
 
       // Parses the parameter array.
-      if (!param_parser.parse_array_decl(ss)) {
+      if (!param_parser_.parse_array_decl(ss)) {
         return false;
       }
     } else if (is_gate_string(command, gate_type)) {
@@ -344,7 +366,7 @@ bool QASMParser::load_qasm_stream(
       std::vector<int> param_indices(num_params);
       for (int i = 0; i < num_params; ++i) {
         assert(ss.good());
-        int index = param_parser.parse_expr(ss);
+        int index = param_parser_.parse_expr(ss);
         if (index == -1) {
           return false;
         }
@@ -405,6 +427,9 @@ bool QASMParser::load_qasm_stream(
       assert(false);
     }
   }
+
+  // Successfully parsed file.
+  param_parser_.end_file();
   return true;
 }
 
diff --git a/src/test/test_qasm_parser.cpp b/src/test/test_qasm_parser.cpp
index 4b33ae56..ac143157 100644
--- a/src/test/test_qasm_parser.cpp
+++ b/src/test/test_qasm_parser.cpp
@@ -152,36 +152,75 @@ void test_param_parsing() {
 
   QASMParser parser(&ctx);
 
-  std::string str = "OPENQASM 2.0;\n"
-                    "include \"qelib1.inc\";\n"
-                    "qubit[2] q;\n"
-                    "input array[angle,2] ps;\n"
-                    "input array[float,3] params;\n"
-                    "cx q[0], q[1];\n"
-                    "rx(ps[0]) q[0];\n"
-                    "rx(ps[1]) q[1];\n"
-                    "rx(params[0]) q[0];\n"
-                    "rx(params[1]) q[1];\n";
+  // Tests parsing a first file.
+  std::string str1 = "OPENQASM 3;\n"
+                     "include \"stdgates.inc\";\n"
+                     "qubit[2] q;\n"
+                     "input array[angle,2] ps;\n"
+                     "input array[float,3] params;\n"
+                     "cx q[0], q[1];\n"
+                     "rx(ps[0]) q[0];\n"
+                     "rx(ps[1]) q[1];\n"
+                     "rx(params[0]) q[0];\n"
+                     "rx(params[1]) q[1];\n";
 
   CircuitSeq *seq1 = nullptr;
-  bool res1 = parser.load_qasm_str(str, seq1);
+  bool res1 = parser.load_qasm_str(str1, seq1);
   if (!res1) {
     std::cout << "Parsing failed with parameter variables." << std::endl;
     assert(false);
     return;
   }
 
-  int pnum = ctx.get_num_parameters();
-  if (pnum != 5) {
-    std::cout << "Unexpected parameter total: " << pnum << "." << std::endl;
+  int pnum1 = ctx.get_num_parameters();
+  if (pnum1 != 5) {
+    std::cout << "Unexpected parameter total: " << pnum1 << "." << std::endl;
     assert(false);
   }
 
-  int input_num = seq1->get_input_param_indices(&ctx).size();
-  if (input_num != 4) {
-    std::cout << "Unexpected input count: " << input_num << "." << std::endl;
+  int input_num1 = seq1->get_input_param_indices(&ctx).size();
+  if (input_num1 != 4) {
+    std::cout << "Unexpected input count: " << input_num1 << "." << std::endl;
     assert(false);
   }
+
+  // Tests parsing a second file.
+  std::string str2 = "OPENQASM 3;\n"
+                     "include \"stdgates.inc\";\n"
+                     "qubit[5] q;\n"
+                     "input array[angle,2] ps;\n"
+                     "cx q[0], q[1];\n"
+                     "rx(ps[0]) q[0];\n"
+                     "rx(ps[1]) q[1];\n";
+
+  CircuitSeq *seq2 = nullptr;
+  bool res2 = parser.load_qasm_str(str2, seq2);
+  if (!res2) {
+    std::cout << "Parsing failed with parameter variables." << std::endl;
+    assert(false);
+    return;
+  }
+
+  int pnum2 = ctx.get_num_parameters();
+  if (pnum2 != 5) {
+    std::cout << "Unexpected parameter total: " << pnum2 << "." << std::endl;
+    assert(false);
+  }
+
+  int input_num2 = seq2->get_input_param_indices(&ctx).size();
+  if (input_num2 != 2) {
+    std::cout << "Unexpected input count: " << input_num2 << "." << std::endl;
+    assert(false);
+  }
+
+  // Checks that parameters were reused.
+  auto all_indices = seq1->get_input_param_indices(&ctx);
+  for (auto j : seq2->get_input_param_indices(&ctx)) {
+    if (std::count(all_indices.begin(), all_indices.end(), j) == 0) {
+      std::cout << "Unexpected parameter: " << j << "." << std::endl;
+      assert(false);
+    }
+  }
 }
 
 int main() {