diff --git a/cJSON.c b/cJSON.c
index 727e1827c..822c10900 100644
--- a/cJSON.c
+++ b/cJSON.c
@@ -42,6 +42,7 @@
 #include <stdlib.h>
 #include <limits.h>
 #include <ctype.h>
+#include <stdint.h>
 
 #ifdef ENABLE_LOCALES
 #include <locale.h>
@@ -394,6 +395,11 @@ static unsigned char* ensure(printbuffer * const p, size_t needed)
         return NULL;
     }
 
+    /* Ensure adding (p->offset + 1) won't overflow SIZE_MAX */
+    if (p->offset > SIZE_MAX - 1 - needed) {
+        return NULL;
+    }
+
     needed += p->offset + 1;
     if (needed <= p->length)
     {