diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index d5f7a218f4..238beebf3e 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -10,6 +10,7 @@
  * ex_getln.c: Functions for entering and editing an Ex command line.
  */
 
+#include <assert.h>
 #include <errno.h>
 #include <stdbool.h>
 #include <string.h>
@@ -3858,8 +3859,10 @@ expand_shellcmd (
     STRLCPY(buf + l, pat, MAXPATHL - l);
 
     /* Expand matches in one directory of $PATH. */
+    char_u **prev_file = *file;
     ret = expand_wildcards(1, &buf, num_file, file, flags);
     if (ret == OK) {
+      assert(*file != prev_file);
       ga_grow(&ga, *num_file);
       {
         for (i = 0; i < *num_file; ++i) {