diff --git a/tests/integrated/test-drift-instability/runtest b/tests/integrated/test-drift-instability/runtest
index 4d5c6a62624b135d58fcd6f58fc541e743a03fbe..3107f85402eb55edd695b74666d3f131c8d66c56 100755
--- a/tests/integrated/test-drift-instability/runtest
+++ b/tests/integrated/test-drift-instability/runtest
@@ -70,7 +70,7 @@ def run_zeff_case(zeff):
         timestep = 1e3
 
     # Delete old output files
-    shell("rm data/BOUT.dmp.*.nc")
+    shell("rm -f data/BOUT.dmp.*.nc")
 
     print("Running drift instability test, zeff = ", zeff)