diff --git a/libc/bionic/mmap.cpp b/libc/bionic/mmap.cpp
index 8f25a89..794f50f 100644
--- a/libc/bionic/mmap.cpp
+++ b/libc/bionic/mmap.cpp
@@ -30,6 +30,7 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include "private/bionic_macros.h"
 #include "private/ErrnoRestorer.h"
 
 // mmap2(2) is like mmap(2), but the offset is in 4096-byte blocks, not bytes.
@@ -45,6 +46,13 @@
     return MAP_FAILED;
   }
 
+  // prevent allocations large enough for `end - start` to overflow
+  size_t rounded = BIONIC_ALIGN(size, PAGE_SIZE);
+  if (rounded < size || size > PTRDIFF_MAX) {
+    errno = ENOMEM;
+    return MAP_FAILED;
+  }
+
   bool is_private_anonymous = (flags & (MAP_PRIVATE | MAP_ANONYMOUS)) != 0;
   void* result = __mmap2(addr, size, prot, flags, fd, offset >> MMAP2_SHIFT);