Index: llvm/trunk/lib/Support/FileCheck.cpp
===================================================================
--- llvm/trunk/lib/Support/FileCheck.cpp
+++ llvm/trunk/lib/Support/FileCheck.cpp
@@ -580,8 +580,10 @@
     for (const auto &Substitution : Substitutions) {
       // Substitute and check for failure (e.g. use of undefined variable).
       Expected<std::string> Value = Substitution->getResult();
-      if (!Value)
+      if (!Value) {
+        Context->LineVariable->clearValue();
         return Value.takeError();
+      }
 
       // Plop it into the regex at the adjusted offset.
       TmpStr.insert(TmpStr.begin() + Substitution->getIndex() + InsertOffset,
Index: llvm/trunk/unittests/Support/FileCheckTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/FileCheckTest.cpp
+++ llvm/trunk/unittests/Support/FileCheckTest.cpp
@@ -334,6 +334,21 @@
   EXPECT_TRUE(Tester.matchExpect("19 21"));
   EXPECT_TRUE(Tester.matchExpect("18 21"));
   EXPECT_FALSE(Tester.matchExpect("18 20"));
+
+  // Check matching a numeric expression using @LINE after match failure uses
+  // the correct value for @LINE.
+  Tester.initNextPattern();
+  EXPECT_FALSE(Tester.parsePatternExpect("[[#@LINE]]"));
+  // Ok, @LINE is 4 now.
+  EXPECT_FALSE(Tester.matchExpect("4"));
+  Tester.initNextPattern();
+  // @LINE is now 5, match with substitution failure.
+  EXPECT_FALSE(Tester.parsePatternExpect("[[#UNKNOWN]]"));
+  EXPECT_TRUE(Tester.matchExpect("FOO"));
+  Tester.initNextPattern();
+  // Check that @LINE is 6 as expected.
+  EXPECT_FALSE(Tester.parsePatternExpect("[[#@LINE]]"));
+  EXPECT_FALSE(Tester.matchExpect("6"));
 }
 
 TEST_F(FileCheckTest, Substitution) {