--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -10,6 +10,7 @@
 #include "postgres.h"

 #include <ctype.h>
+#include <sys/stat.h>
 #include <unistd.h>

 #include "common/file_utils.h"
@@ -237,6 +238,18 @@ ParseConfigFile(const char *config_file, bool strict,
        }

        fp = AllocateFile(abs_path, "r");
+       if (fp)
+       {
+               struct stat st;
+
+               if (fstat(fileno(fp), &st) == 0 && S_ISDIR(st.st_mode))
+               {
+                       FreeFile(fp);
+                       fp = NULL;
+                       errno = EISDIR;
+               }
+       }
+
        if (!fp)
        {
                if (strict)