diff --git a/memory/mozalloc/cxxalloc.cpp b/memory/mozalloc/cxxalloc.cpp
index 07ebef7f35af..41f419fe2dd6 100644
--- a/memory/mozalloc/cxxalloc.cpp
+++ b/memory/mozalloc/cxxalloc.cpp
@@ -15,7 +15,7 @@
 
 #include "mozilla/Attributes.h"
 
-extern "C" MFBT_API void* moz_xmalloc(size_t size) MOZ_ALLOCATOR;
+extern "C" MFBT_API void* moz_xmalloc(size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
 namespace std {
 struct nothrow_t;
diff --git a/memory/mozalloc/mozalloc.h b/memory/mozalloc/mozalloc.h
index a80afbd5b0eb..74af281d294e 100644
--- a/memory/mozalloc/mozalloc.h
+++ b/memory/mozalloc/mozalloc.h
@@ -75,21 +75,24 @@ MOZ_BEGIN_EXTERN_C
  * passing that pointer to |free()|.
  */
 
-MFBT_API void* moz_xmalloc(size_t size) MOZ_ALLOCATOR;
+MFBT_API void* moz_xmalloc(size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
-MFBT_API void* moz_xcalloc(size_t nmemb, size_t size) MOZ_ALLOCATOR;
+MFBT_API void* moz_xcalloc(size_t nmemb, size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
-MFBT_API void* moz_xrealloc(void* ptr, size_t size) MOZ_ALLOCATOR;
+MFBT_API void* moz_xrealloc(void* ptr, size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
-MFBT_API char* moz_xstrdup(const char* str) MOZ_ALLOCATOR;
+MFBT_API char* moz_xstrdup(const char* str) MOZ_INFALLIBLE_ALLOCATOR;
 
 #if defined(HAVE_STRNDUP)
-MFBT_API char* moz_xstrndup(const char* str, size_t strsize) MOZ_ALLOCATOR;
+MFBT_API char* moz_xstrndup(const char* str,
+                            size_t strsize) MOZ_INFALLIBLE_ALLOCATOR;
 #endif /* if defined(HAVE_STRNDUP) */
 
-MFBT_API void* moz_xmemdup(const void* ptr, size_t size) MOZ_ALLOCATOR;
+MFBT_API void* moz_xmemdup(const void* ptr,
+                           size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
-MFBT_API void* moz_xmemalign(size_t boundary, size_t size) MOZ_ALLOCATOR;
+MFBT_API void* moz_xmemalign(size_t boundary,
+                             size_t size) MOZ_INFALLIBLE_ALLOCATOR;
 
 MFBT_API size_t moz_malloc_usable_size(void* ptr);
 
diff --git a/mfbt/Attributes.h b/mfbt/Attributes.h
index 62cde0a1768b..84341f59f2f9 100644
--- a/mfbt/Attributes.h
+++ b/mfbt/Attributes.h
@@ -353,8 +353,11 @@
  */
 #if defined(__GNUC__) || defined(__clang__)
 #  define MOZ_ALLOCATOR __attribute__((malloc, warn_unused_result))
+#  define MOZ_INFALLIBLE_ALLOCATOR \
+    __attribute__((malloc, warn_unused_result, returns_nonnull))
 #else
 #  define MOZ_ALLOCATOR
+#  define MOZ_INFALLIBLE_ALLOCATOR
 #endif
 
 /**