diff --git a/llvm/include/llvm/Support/FileCheck.h b/llvm/include/llvm/Support/FileCheck.h
--- a/llvm/include/llvm/Support/FileCheck.h
+++ b/llvm/include/llvm/Support/FileCheck.h
@@ -61,7 +61,10 @@
   CheckBadNot,
 
   /// Marks when parsing found a -COUNT directive with invalid count value.
-  CheckBadCount
+  CheckBadCount,
+
+  /// Marks when parsing found a directive followed by whitespace (not a colon).
+  CheckBadColon,
 };
 
 class FileCheckType {
diff --git a/llvm/lib/Support/FileCheck.cpp b/llvm/lib/Support/FileCheck.cpp
--- a/llvm/lib/Support/FileCheck.cpp
+++ b/llvm/lib/Support/FileCheck.cpp
@@ -1088,6 +1088,8 @@
     return "bad NOT";
   case Check::CheckBadCount:
     return "bad COUNT";
+  case Check::CheckBadColon:
+    return "bad colon";
   }
   llvm_unreachable("unknown FileCheckType");
 }
@@ -1104,6 +1106,9 @@
   if (NextChar == ':')
     return {Check::CheckPlain, Rest};
 
+  if (NextChar == ' ' || NextChar == '\t')
+    return {Check::CheckBadColon, Rest};
+
   if (NextChar != '-')
     return {Check::CheckNone, StringRef()};
 
@@ -1144,6 +1149,11 @@
       Rest.startswith("EMPTY-NOT:") || Rest.startswith("NOT-EMPTY:"))
     return {Check::CheckBadNot, Rest};
 
+  if (Rest.consume_front("NEXT") || Rest.consume_front("SAME") ||
+      Rest.consume_front("NOT") || Rest.consume_front("DAG") ||
+      Rest.consume_front("LABEL") || Rest.consume_front("EMPTY"))
+    return {Check::CheckBadColon, Rest};
+
   return {Check::CheckNone, Rest};
 }
 
@@ -1306,6 +1316,14 @@
       return true;
     }
 
+    // Complain about directives that are not followed immediately by a colon.
+    if (CheckTy == Check::CheckBadColon) {
+      SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Error,
+                      "colon required after check directive '" + UsedPrefix +
+                          "'");
+      return true;
+    }
+
     // Complain about invalid count specification.
     if (CheckTy == Check::CheckBadCount) {
       SM.PrintMessage(SMLoc::getFromPointer(Buffer.data()), SourceMgr::DK_Error,
diff --git a/llvm/utils/FileCheck/FileCheck.cpp b/llvm/utils/FileCheck/FileCheck.cpp
--- a/llvm/utils/FileCheck/FileCheck.cpp
+++ b/llvm/utils/FileCheck/FileCheck.cpp
@@ -287,6 +287,8 @@
     return "bad-not";
   case Check::CheckBadCount:
     return "bad-count";
+  case Check::CheckBadColon:
+    return "bad-colon";
   case Check::CheckNone:
     llvm_unreachable("invalid FileCheckType");
   }