diff --git a/smodels/lib/pythia8/Makefile b/smodels/lib/pythia8/Makefile
index 26ef5ef30..037d2945b 100644
--- a/smodels/lib/pythia8/Makefile
+++ b/smodels/lib/pythia8/Makefile
@@ -20,6 +20,7 @@ install_pythia8:
 	./installer.py
 
 clean:
+	chmod -R u+w pythia$(PYTHIAVER)
 	rm -rf $(EXES) test.slha pythia$(PYTHIAVER) .pythia*.tgz* pythia*.tgz*  pythia8.exe events.lhe
 
 pythia8.exe: pythia8.cc .PHONY
diff --git a/smodels/lib/pythia8/installer.py b/smodels/lib/pythia8/installer.py
index 0f92673fa..d18a28b5a 100755
--- a/smodels/lib/pythia8/installer.py
+++ b/smodels/lib/pythia8/installer.py
@@ -133,7 +133,7 @@ def checkPythiaHeaderFile():
     return True
 
 def compilePythia():
-    """ finally, compile pythia """
+    """ compile pythia """
     ver = getVersion()
     ncpus = max ( 1, getNCPUs()-2 )
     cmd = f"cd pythia{ver}; ./configure ; make -j {ncpus}"
@@ -145,6 +145,15 @@ def compilePythia():
         sys.stdout.buffer.write(c)
         sys.stdout.buffer.flush()
 
+def fixACLs():
+    """ finally, remove all writable flags from install. when running 
+    many pythia8 instances in parallel, for some reason they sometimes deleted
+    files from the install, making the install unusable """
+    # print ( f"fixACLs: {os.getcwd()}" )
+    cmd = "chmod -R a-w pythia8308"
+    import subprocess
+    subprocess.getoutput ( cmd )
+
 def installPythia():
     """ fetch tarball, unzip it, compile pythia """
     if checkPythia() and checkPythiaHeaderFile():
@@ -156,6 +165,7 @@ def installPythia():
     fetch()
     unzip()
     compilePythia()
+    fixACLs()
     rmTarball()
 
 if __name__ == "__main__":