diff --git a/mfbt/tests/TestPair.cpp b/mfbt/tests/TestPair.cpp
index f1fa9c554f11..c8017674e8ff 100644
--- a/mfbt/tests/TestPair.cpp
+++ b/mfbt/tests/TestPair.cpp
@@ -33,13 +33,27 @@ INSTANTIATE(int, int, prim1, 2 * sizeof(int));
 INSTANTIATE(int, long, prim2, 2 * sizeof(long));
 
 struct EmptyClass { explicit EmptyClass(int) {} };
-struct NonEmpty { char mC; explicit NonEmpty(int) {} };
+struct NonEmpty
+{
+  char mC;
+  explicit NonEmpty(int)
+    : mC('\0')
+  {
+  }
+};
 
 INSTANTIATE(int, EmptyClass, both1, sizeof(int));
 INSTANTIATE(int, NonEmpty, both2, 2 * sizeof(int));
 INSTANTIATE(EmptyClass, NonEmpty, both3, 1);
 
-struct A { char dummy; explicit A(int) {} };
+struct A
+{
+  char dummy;
+  explicit A(int)
+    : dummy('\0')
+  {
+  }
+};
 struct B : A { explicit B(int aI) : A(aI) {} };
 
 INSTANTIATE(A, A, class1, 2);