diff --git a/lib/tsan/rtl/tsan_mman.cc b/lib/tsan/rtl/tsan_mman.cc
index cbfb67a..1d9644e 100644
--- a/lib/tsan/rtl/tsan_mman.cc
+++ b/lib/tsan/rtl/tsan_mman.cc
@@ -143,20 +143,16 @@
 }
 
 void *user_realloc(ThreadState *thr, uptr pc, void *p, uptr sz) {
-  void *p2 = 0;
   // FIXME: Handle "shrinking" more efficiently,
   // it seems that some software actually does this.
-  if (sz) {
-    p2 = user_alloc(thr, pc, sz);
-    if (p2 == 0)
-      return 0;
-    if (p) {
-      uptr oldsz = user_alloc_usable_size(p);
-      internal_memcpy(p2, p, min(oldsz, sz));
-    }
-  }
-  if (p)
+  void *p2 = user_alloc(thr, pc, sz);
+  if (p2 == 0)
+    return 0;
+  if (p) {
+    uptr oldsz = user_alloc_usable_size(p);
+    internal_memcpy(p2, p, min(oldsz, sz));
     user_free(thr, pc, p);
+  }
   return p2;
 }
 
diff --git a/lib/tsan/tests/unit/tsan_mman_test.cc b/lib/tsan/tests/unit/tsan_mman_test.cc
index 609141c..60dea3d 100644
--- a/lib/tsan/tests/unit/tsan_mman_test.cc
+++ b/lib/tsan/tests/unit/tsan_mman_test.cc
@@ -53,9 +53,9 @@
   uptr pc = 0;
   {
     void *p = user_realloc(thr, pc, 0, 0);
-    // Strictly saying this is incorrect, realloc(NULL, N) is equivalent to
-    // malloc(N), thus must return non-NULL pointer.
-    EXPECT_EQ(p, (void*)0);
+    // Realloc(NULL, N) is equivalent to malloc(N), thus must return
+    // non-NULL pointer.
+    EXPECT_NE(p, (void*)0);
   }
   {
     void *p = user_realloc(thr, pc, 0, 100);
@@ -68,7 +68,7 @@
     EXPECT_NE(p, (void*)0);
     memset(p, 0xde, 100);
     void *p2 = user_realloc(thr, pc, p, 0);
-    EXPECT_EQ(p2, (void*)0);
+    EXPECT_NE(p2, (void*)0);
   }
   {
     void *p = user_realloc(thr, pc, 0, 100);
diff --git a/test/tsan/Darwin/realloc-zero.cc b/test/tsan/Darwin/realloc-zero.cc
new file mode 100644
index 0000000..9826246
--- /dev/null
+++ b/test/tsan/Darwin/realloc-zero.cc
@@ -0,0 +1,20 @@
+// Test that realloc(nullptr, 0) return a non-NULL pointer.
+
+// RUN: %clang_tsan %s -o %t
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#include <malloc/malloc.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+
+int main() {
+  void *p = realloc(NULL, 0);
+  if (!p) {
+    abort();
+  }
+  fprintf(stderr, "Okay.\n");
+  return 0;
+}
+
+// CHECK: Okay.