diff --git a/compiler-rt/test/hwasan/TestCases/many-threads-uaf.c b/compiler-rt/test/hwasan/TestCases/many-threads-uaf.c
index 8fa07861371d5..e02ab5b28ce04 100644
--- a/compiler-rt/test/hwasan/TestCases/many-threads-uaf.c
+++ b/compiler-rt/test/hwasan/TestCases/many-threads-uaf.c
@@ -23,6 +23,7 @@ void *BoringThread(void *arg) {
 void *UAFThread(void *arg) {
   char * volatile x = (char*)malloc(10);
   fprintf(stderr, "ZZZ %p\n", x);
+  fflush(stderr);
   free(x);
   x[5] = 42;
   // CHECK: ERROR: HWAddressSanitizer: tag-mismatch on address
diff --git a/compiler-rt/test/hwasan/TestCases/mem-intrinsics.c b/compiler-rt/test/hwasan/TestCases/mem-intrinsics.c
index 78bef538af116..da1cb68696920 100644
--- a/compiler-rt/test/hwasan/TestCases/mem-intrinsics.c
+++ b/compiler-rt/test/hwasan/TestCases/mem-intrinsics.c
@@ -21,6 +21,7 @@ int main() {
   memcpy(Q, P, 32);
 #endif
   write(STDOUT_FILENO, "recovered\n", 10);
+  fflush(stdout);
   // WRITE: ERROR: HWAddressSanitizer: tag-mismatch on address
   // WRITE: WRITE of size 32 at {{.*}} tags: [[PTR_TAG:..]]/[[MEM_TAG:..]] (ptr/mem)
   // WRITE: Invalid access starting at offset 16
diff --git a/compiler-rt/test/hwasan/TestCases/use-after-free.c b/compiler-rt/test/hwasan/TestCases/use-after-free.c
index 070622f560a22..b4b79875e8111 100644
--- a/compiler-rt/test/hwasan/TestCases/use-after-free.c
+++ b/compiler-rt/test/hwasan/TestCases/use-after-free.c
@@ -15,6 +15,7 @@ int main() {
   free(x);
   __hwasan_disable_allocator_tagging();
   fprintf(stderr, ISREAD ? "Going to do a READ\n" : "Going to do a WRITE\n");
+  fflush(stderr);
   // CHECK: Going to do a [[TYPE:[A-Z]*]]
   int r = 0;
   if (ISREAD) r = x[5]; else x[5] = 42;  // should be on the same line.