diff --git a/magnets.c b/magnets.c
index 2679eb4..0379fa0 100644
--- a/magnets.c
+++ b/magnets.c
@@ -36,6 +36,7 @@
 #include <string.h>
 #include <assert.h>
 #include <ctype.h>
+#include <limits.h>
 #include <math.h>
 
 #include "puzzles.h"
@@ -232,6 +233,8 @@ static const char *validate_params(const game_params *params, bool full)
 {
     if (params->w < 2) return "Width must be at least two";
     if (params->h < 2) return "Height must be at least two";
+    if (params->w > INT_MAX / params->h)
+        return "Width times height must not be unreasonably large";
     if (params->diff >= DIFF_TRICKY) {
         if (params->w < 5 && params->h < 5)
             return "Either width or height must be at least five for Tricky";