diff --git a/tests/gdb-tests/tests.sh b/tests/gdb-tests/tests.sh
index 46b05fc8b..b07f27fd8 100755
--- a/tests/gdb-tests/tests.sh
+++ b/tests/gdb-tests/tests.sh
@@ -32,7 +32,8 @@ while [[ $# -gt 0 ]]; do
     case $1 in
         -p | --pdb)
             USE_PDB=1
-            echo "Will run tests with Python debugger"
+	    SERIAL=1
+            echo "Will run tests in serial and with Python debugger"
             shift
             ;;
         -c | --cov)