diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -10845,8 +10845,10 @@
   if (S.Diags.getSuppressSystemWarnings() && S.SourceMgr.isInSystemMacro(Loc))
     return;
 
-  S.Diag(Loc, diag::warn_pointer_sub_null_ptr)
-      << S.getLangOpts().CPlusPlus << Pointer->getSourceRange();
+  S.DiagRuntimeBehavior(Loc, Pointer,
+                        S.PDiag(diag::warn_pointer_sub_null_ptr)
+                            << S.getLangOpts().CPlusPlus
+                            << Pointer->getSourceRange());
 }
 
 /// Diagnose invalid arithmetic on two function pointers.
diff --git a/clang/test/Sema/pointer-subtraction.c b/clang/test/Sema/pointer-subtraction.c
--- a/clang/test/Sema/pointer-subtraction.c
+++ b/clang/test/Sema/pointer-subtraction.c
@@ -11,6 +11,16 @@
   f = (char *)(f - (char *)0);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
   f = (char *)((char *)0 - (char *)0); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}} expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
 
+  if (1)
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+  else
+    f = (char *)((char *)0 - f);
+
+  if (0)
+    f = (char *)((char *)0 - f);
+  else
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+
 #ifndef SYSTEM_WARNINGS
   SYSTEM_MACRO(f);
 #else
diff --git a/clang/test/Sema/pointer-subtraction.cpp b/clang/test/Sema/pointer-subtraction.cpp
--- a/clang/test/Sema/pointer-subtraction.cpp
+++ b/clang/test/Sema/pointer-subtraction.cpp
@@ -11,6 +11,16 @@
   f = (char *)(f - (char *)0);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
   f = (char *)((char *)0 - (char *)0); // valid in C++
 
+  if (1)
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+  else
+    f = (char *)((char *)0 - f);
+
+  if (0)
+    f = (char *)((char *)0 - f);
+  else
+    f = (char *)((char *)0 - f);         // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+
 #ifndef SYSTEM_WARNINGS
   SYSTEM_MACRO(f);
 #else