diff --git a/libc/test/IntegrationTest/test.cpp b/libc/test/IntegrationTest/test.cpp
--- a/libc/test/IntegrationTest/test.cpp
+++ b/libc/test/IntegrationTest/test.cpp
@@ -57,6 +57,7 @@
 // which just hands out continuous blocks from a statically allocated chunk of
 // memory.
 
+static constexpr uint64_t memory_size = 16384;
 static uint8_t memory[16384];
 static uint8_t *ptr = memory;
 
@@ -65,7 +66,7 @@
 void *malloc(size_t s) {
   void *mem = ptr;
   ptr += s;
-  return mem;
+  return static_cast<uint64_t>(ptr - memory) >= memory_size ? nullptr : mem;
 }
 
 void free(void *) {}
diff --git a/libc/test/UnitTest/HermeticTestUtils.cpp b/libc/test/UnitTest/HermeticTestUtils.cpp
--- a/libc/test/UnitTest/HermeticTestUtils.cpp
+++ b/libc/test/UnitTest/HermeticTestUtils.cpp
@@ -29,7 +29,8 @@
 // requires. Hence, as a work around for this problem, we use a simple allocator
 // which just hands out continuous blocks from a statically allocated chunk of
 // memory.
-static uint8_t memory[16384];
+static constexpr uint64_t memory_size = 16384;
+static uint8_t memory[memory_size];
 static uint8_t *ptr = memory;
 
 } // anonymous namespace
@@ -68,7 +69,7 @@
   s = ((s + ALIGNMENT - 1) / ALIGNMENT) * ALIGNMENT;
   void *mem = ptr;
   ptr += s;
-  return mem;
+  return static_cast<uint64_t>(ptr - memory) >= memory_size ? nullptr : mem;
 }
 
 void free(void *) {}