diff --git a/lib/Parse/ParseIfConfig.cpp b/lib/Parse/ParseIfConfig.cpp
index 878f5b3e64f88..611b5b14f2735 100644
--- a/lib/Parse/ParseIfConfig.cpp
+++ b/lib/Parse/ParseIfConfig.cpp
@@ -321,6 +321,8 @@ class ValidateIfConfigCondition :
                    diag::unsupported_platform_runtime_condition_argument);
         return nullptr;
       }
+
+      // Just a warning for other unsupported arguments.
       StringRef DiagName;
       switch (*Kind) {
       case PlatformConditionKind::OS:
@@ -338,7 +340,6 @@ class ValidateIfConfigCondition :
       for (auto suggestion : suggestions)
         D.diagnose(Loc, diag::note_typo_candidate, suggestion)
           .fixItReplace(Arg->getSourceRange(), suggestion);
-      return nullptr;
     }
 
     return E;
diff --git a/test/Parse/ConditionalCompilation/basicParseErrors.swift b/test/Parse/ConditionalCompilation/basicParseErrors.swift
index d853e4b4c43ed..6ea3db58c51ed 100644
--- a/test/Parse/ConditionalCompilation/basicParseErrors.swift
+++ b/test/Parse/ConditionalCompilation/basicParseErrors.swift
@@ -114,3 +114,27 @@ undefinedFunc() // ignored.
 #else
 undefinedFunc() // expected-error {{use of unresolved identifier 'undefinedFunc'}}
 #endif
+
+/// Invalid platform condition arguments don't invalidate the whole condition.
+#if !arch(tecture) && !os(ystem) && !_endian(ness)
+// expected-warning@-1 {{unknown architecture for build configuration 'arch'}}
+// expected-note@-2 {{did you mean 'arm'?}} {{11-18=arm}}
+// expected-warning@-3 {{unknown operating system for build configuration 'os'}}
+// expected-note@-4 {{did you mean 'OSX'?}} {{27-32=OSX}}
+// expected-note@-5 {{did you mean 'PS4'?}} {{27-32=PS4}}
+// expected-warning@-6 {{unknown endianness for build configuration '_endian'}}
+// expected-note@-7 {{did you mean 'big'?}} {{46-50=big}}
+func fn_k() {}
+#endif
+fn_k()
+
+#if os(cillator) || arch(ive)
+// expected-warning@-1 {{unknown operating system for build configuration 'os'}}
+// expected-note@-2 {{did you mean 'macOS'?}} {{8-16=macOS}}
+// expected-note@-3 {{did you mean 'iOS'?}} {{8-16=iOS}}
+// expected-warning@-4 {{unknown architecture for build configuration 'arch'}}
+// expected-note@-5 {{did you mean 'arm'?}} {{26-29=arm}}
+// expected-note@-6 {{did you mean 'i386'?}} {{26-29=i386}}
+func undefinedFunc() // ignored.
+#endif
+undefinedFunc() // expected-error {{use of unresolved identifier 'undefinedFunc'}}