diff --git a/xdelta3/testing/file.h b/xdelta3/testing/file.h
index 19b4688..55b0eb8 100644
--- a/xdelta3/testing/file.h
+++ b/xdelta3/testing/file.h
@@ -314,7 +314,7 @@ class ExtFile {
     pid_t pid = getpid();
     char buf[64];
     xoff_t xpid = pid;
-    snprintf(buf, 64, "/tmp/regtest.%"Q"u.%d", xpid, static_counter++);
+    snprintf(buf, 64, "/tmp/regtest.%" Q "u.%d", xpid, static_counter++);
     filename_.append(buf);
     unlink(filename_.c_str());
   }