Index: lib/asan/CMakeLists.txt
===================================================================
--- lib/asan/CMakeLists.txt
+++ lib/asan/CMakeLists.txt
@@ -64,6 +64,14 @@
   -ftls-model=initial-exec ASAN_DYNAMIC_CFLAGS)
 append_list_if(MSVC /DEBUG ASAN_DYNAMIC_LINK_FLAGS)
 
+# Delay load dbghelp. Newer versions of dbghelp depend on ucrtbase.dll. We
+# can't allow ucrtbase.dll to initialize before ASan, or some heap allocations
+# will not be intercepted (http://llvm.org/pr30903). The loader initializes
+# dependencies before dependent DLLs, so we can't have a direct dependence on
+# dbghelp.
+append_list_if(MSVC -delayload:dbghelp.dll ASAN_DYNAMIC_LINK_FLAGS)
+append_list_if(MSVC -defaultlib:delayimp.lib ASAN_DYNAMIC_LINK_FLAGS)
+
 append_list_if(COMPILER_RT_HAS_LIBC c ASAN_DYNAMIC_LIBS)
 append_list_if(COMPILER_RT_HAS_LIBDL dl ASAN_DYNAMIC_LIBS)
 append_list_if(COMPILER_RT_HAS_LIBRT rt ASAN_DYNAMIC_LIBS)
Index: test/asan/TestCases/Windows/delay_dbghelp.cc
===================================================================
--- /dev/null
+++ test/asan/TestCases/Windows/delay_dbghelp.cc
@@ -0,0 +1,19 @@
+// Make a directory, copy the problematic copies of dbg*.dll into that
+// directory, build an exe there, and force the loader to find dbghelp.dll there
+// instead of searching in C:/Windows/system32 first. Touching t.exe.local does
+// this, according to MSDN:
+// https://msdn.microsoft.com/en-us/library/windows/desktop/ms682600(v=vs.85).aspx
+//
+// RUN: rm -rf %t.dir && mkdir %t.dir && cd %t.dir
+// RUN: find %/S/Inputs/delay_dbghelp -iname '*.dll' | xargs cp -t .
+// RUN: touch t.exe.local
+// RUN: %clang_cl_asan %s -Fet.exe
+// RUN: %run %t.dir/t.exe
+
+// REQUIRES: asan-64-bits
+
+extern "C" int puts(const char *);
+
+int main() {
+  puts("main");
+}