diff --git a/cores/esp8266/umm_malloc/umm_malloc.c b/cores/esp8266/umm_malloc/umm_malloc.c
index 030042a1fc..ac249b643d 100644
--- a/cores/esp8266/umm_malloc/umm_malloc.c
+++ b/cores/esp8266/umm_malloc/umm_malloc.c
@@ -1685,7 +1685,9 @@ void *umm_calloc( size_t num, size_t item_size ) {
 
   size += POISON_SIZE(size);
   ret = _umm_malloc(size);
-  memset(ret, 0x00, size);
+  if (ret) {
+    memset(ret, 0x00, size);
+  }
 
   ret = GET_POISONED(ret, size);