diff --git a/compiler-rt/lib/lsan/lsan_allocator.cpp b/compiler-rt/lib/lsan/lsan_allocator.cpp
--- a/compiler-rt/lib/lsan/lsan_allocator.cpp
+++ b/compiler-rt/lib/lsan/lsan_allocator.cpp
@@ -123,14 +123,18 @@
 
 void *Reallocate(const StackTrace &stack, void *p, uptr new_size,
                  uptr alignment) {
-  RegisterDeallocation(p);
   if (new_size > max_malloc_size) {
-    allocator.Deallocate(GetAllocatorCache(), p);
-    return ReportAllocationSizeTooBig(new_size, stack);
+    ReportAllocationSizeTooBig(new_size, stack);
+    return nullptr;
   }
-  p = allocator.Reallocate(GetAllocatorCache(), p, new_size, alignment);
-  RegisterAllocation(stack, p, new_size);
-  return p;
+  RegisterDeallocation(p);
+  void *new_p =
+      allocator.Reallocate(GetAllocatorCache(), p, new_size, alignment);
+  if (new_p)
+    RegisterAllocation(stack, new_p, new_size);
+  else if (new_size != 0)
+    RegisterAllocation(stack, p, new_size);
+  return new_p;
 }
 
 void GetAllocatorCacheRange(uptr *begin, uptr *end) {
diff --git a/compiler-rt/test/lsan/TestCases/malloc_zero.c b/compiler-rt/test/lsan/TestCases/malloc_zero.c
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/lsan/TestCases/malloc_zero.c
@@ -0,0 +1,20 @@
+// RUN: %clang_lsan %s -o %t
+// RUN: %env_lsan_opts=use_stacks=0 not %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+#include <stdlib.h>
+
+// CHECK: {{Leak|Address}}Sanitizer: detected memory leaks
+// CHECK: {{Leak|Address}}Sanitizer: 1 byte(s) leaked in 1 allocation(s).
+
+__attribute__((noinline))
+void test() {
+  // The behavior of malloc(0) is implementation-defined.
+  char *p = malloc(0);
+  fprintf(stderr, "zero: %p\n", p);
+  p = 0;
+}
+
+int main() {
+  test();
+}
diff --git a/compiler-rt/test/lsan/TestCases/realloc_too_big.c b/compiler-rt/test/lsan/TestCases/realloc_too_big.c
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/lsan/TestCases/realloc_too_big.c
@@ -0,0 +1,23 @@
+// RUN: %clang_lsan %s -o %t
+// RUN: %env_lsan_opts=allocator_may_return_null=1:max_allocation_size_mb=1 not %run %t 2>&1 | FileCheck %s
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// CHECK: {{Leak|Address}}Sanitizer failed to allocate 0x100001 bytes
+
+// CHECK: {{Leak|Address}}Sanitizer: detected memory leaks
+// CHECK: {{Leak|Address}}Sanitizer: 9 byte(s) leaked in 1 allocation(s).
+
+__attribute__((noinline))
+void test() {
+  char *p = malloc(9);
+  fprintf(stderr, "nine: %p\n", p);
+  assert(realloc(p, 0x100001) == NULL); // 1MiB+1
+  p = 0;
+}
+
+int main() {
+  test();
+}
diff --git a/compiler-rt/test/lsan/TestCases/realloc_zero.c b/compiler-rt/test/lsan/TestCases/realloc_zero.c
new file mode 100644
--- /dev/null
+++ b/compiler-rt/test/lsan/TestCases/realloc_zero.c
@@ -0,0 +1,12 @@
+// RUN: %clang_lsan %s -o %t
+// RUN: %run %t
+
+#include <assert.h>
+#include <stdlib.h>
+
+int main() {
+  char *p = malloc(1);
+  // The behavior of realloc(p, 0) is implementation-defined.
+  // We free the allocation.
+  assert(realloc(p, 0) == NULL);
+}