diff --git a/src/libImaging/Mode.c b/src/libImaging/Mode.c
index 659e7aada..1ec24aae8 100644
--- a/src/libImaging/Mode.c
+++ b/src/libImaging/Mode.c
@@ -1,6 +1,10 @@
 #include "Mode.h"
 #include <string.h>
 
+#ifdef NDEBUG
+#include <stdio.h>
+#include <stdlib.h>
+#endif
 
 const ModeData MODES[] = {
     [IMAGING_MODE_UNKNOWN] = {""},
@@ -39,6 +43,11 @@ const ModeID findModeID(const char * const name) {
         return IMAGING_MODE_UNKNOWN;
     }
     for (size_t i = 0; i < sizeof(MODES) / sizeof(*MODES); i++) {
+#ifdef NDEBUG
+        if (MODES[i].name == NULL) {
+            fprintf(stderr, "Mode ID %zu is not defined.\n", (size_t)i);
+        } else
+#endif
         if (strcmp(MODES[i].name, name) == 0) {
             return (ModeID)i;
         }
@@ -238,6 +247,11 @@ const RawModeID findRawModeID(const char * const name) {
         return IMAGING_RAWMODE_UNKNOWN;
     }
     for (size_t i = 0; i < sizeof(RAWMODES) / sizeof(*RAWMODES); i++) {
+#ifdef NDEBUG
+        if (RAWMODES[i].name == NULL) {
+            fprintf(stderr, "Rawmode ID %zu is not defined.\n", (size_t)i);
+        } else
+#endif
         if (strcmp(RAWMODES[i].name, name) == 0) {
             return (RawModeID)i;
         }