diff --git a/lib/internal.h b/lib/internal.h
index cb1d0c4f..b393a85f 100644
--- a/lib/internal.h
+++ b/lib/internal.h
@@ -281,4 +281,6 @@ static inline bool uint64_mult_overflow(uint64_t *u, uint64_t b, size_t size)
 #define KEY_EXTERNAL_VERIFICATION -1
 #define KEY_VERIFIED 0
 
+size_t crypt_safe_alloc_size(const void *data);
+
 #endif /* INTERNAL_H */
diff --git a/lib/utils_safe_memory.c b/lib/utils_safe_memory.c
index 885a5518..5ee68d2d 100644
--- a/lib/utils_safe_memory.c
+++ b/lib/utils_safe_memory.c
@@ -107,3 +107,15 @@ void *crypt_safe_realloc(void *data, size_t size)
 	crypt_safe_free(data);
 	return new_data;
 }
+
+size_t crypt_safe_alloc_size(const void *data)
+{
+	const void *p;
+
+	if (!data)
+		return 0;
+
+	p = (const char *)data - OVERHEAD;
+
+	return ((const struct safe_allocation *)p)->size;
+}