diff --git a/compiler-rt/lib/asan/asan_poisoning.cpp b/compiler-rt/lib/asan/asan_poisoning.cpp
--- a/compiler-rt/lib/asan/asan_poisoning.cpp
+++ b/compiler-rt/lib/asan/asan_poisoning.cpp
@@ -66,6 +66,12 @@
   // Since asan's mapping is compacting, the shadow chunk may be
   // not page-aligned, so we only flush the page-aligned portion.
   ReleaseMemoryPagesToOS(MemToShadow(p), MemToShadow(p + size));
+
+#if SANITIZER_FUCHSIA
+  // In Fuchsia ReleaseMemoryPagesToOS is a no-op. __sanitizer_fill_shadow
+  // With a 0 value and a 0 threshold will decommit the shadow pages.
+  __sanitizer_fill_shadow(p, size, 0, 0);
+#endif
 }
 
 void AsanPoisonOrUnpoisonIntraObjectRedzone(uptr ptr, uptr size, bool poison) {