diff --git a/src/etc/test-float-parse/runtests.py b/src/etc/test-float-parse/runtests.py
index 4d2902e986f56..218552a45972d 100644
--- a/src/etc/test-float-parse/runtests.py
+++ b/src/etc/test-float-parse/runtests.py
@@ -193,10 +193,12 @@ def interact(proc, queue):
 
 def main():
     global MAILBOX
-    tests = [os.path.splitext(f)[0] for f in glob('*.rs')
-                                    if not f.startswith('_')]
+    all_tests = [os.path.splitext(f)[0] for f in glob('*.rs') if not f.startswith('_')]
     args = sys.argv[1:]
-    tests = [test for test in tests if test in args]
+    if args:
+        tests = [test for test in all_tests if test in args]
+    else
+        tests = all_tests
     if not tests:
         print("Error: No tests to run")
         sys.exit(1)