diff --git a/.gitignore b/.gitignore
index 319d66928..9f36e853c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -25,3 +25,4 @@ src/exp
 src/user/CylindricalDisk.cc
 src/user/EllipsoidForce.cc
 src/user/SLSphere.cc
+_codeql_detected_source_root
diff --git a/src/OutHDF5.cc b/src/OutHDF5.cc
index 3d3e9a74a..7259adcaa 100644
--- a/src/OutHDF5.cc
+++ b/src/OutHDF5.cc
@@ -193,13 +193,15 @@ void OutHDF5::initialize()
       else {
 	std::ostringstream fname;
 
-	if (chkpt)
+	if (chkpt) {
 	  fname << outdir
-		<<  "checkpoint_" << runtag << ".1";
-	else
+		<<  "checkpoint_" << runtag;
+	  if (numprocs>1) fname << ".1";
+	} else {
 	  fname << outdir
 		<<  filename << "_" << setw(5) << setfill('0') << nbeg
 		<< ".1";
+	}
 
 	std::filesystem::path file_path = fname.str();