diff --git a/libc/bionic/mmap.cpp b/libc/bionic/mmap.cpp
index 9bc80a2..8301445 100644
--- a/libc/bionic/mmap.cpp
+++ b/libc/bionic/mmap.cpp
@@ -27,6 +27,7 @@
  */
 
 #include <errno.h>
+#include <stdint.h>
 #include <sys/mman.h>
 #include <unistd.h>
 
diff --git a/libc/bionic/mremap.cpp b/libc/bionic/mremap.cpp
index 4892b1d..6653d43 100644
--- a/libc/bionic/mremap.cpp
+++ b/libc/bionic/mremap.cpp
@@ -26,12 +26,24 @@
  * SUCH DAMAGE.
  */
 
+#include <errno.h>
 #include <sys/mman.h>
 #include <stdarg.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include "private/bionic_macros.h"
 
 extern "C" void* ___mremap(void*, size_t, size_t, int, void*);
 
 void* mremap(void* old_address, size_t old_size, size_t new_size, int flags, ...) {
+  // prevent allocations large enough for `end - start` to overflow
+  size_t rounded = BIONIC_ALIGN(new_size, PAGE_SIZE);
+  if (rounded < new_size || rounded > PTRDIFF_MAX) {
+    errno = ENOMEM;
+    return MAP_FAILED;
+  }
+
   void* new_address = nullptr;
   // The optional argument is only valid if the MREMAP_FIXED flag is set,
   // so we assume it's not present otherwise.