diff --git a/llvm/include/llvm/FileCheck/FileCheck.h b/llvm/include/llvm/FileCheck/FileCheck.h
--- a/llvm/include/llvm/FileCheck/FileCheck.h
+++ b/llvm/include/llvm/FileCheck/FileCheck.h
@@ -30,6 +30,7 @@
   std::vector<StringRef> ImplicitCheckNot;
   std::vector<StringRef> GlobalDefines;
   bool AllowEmptyInput = false;
+  bool AllowUnusedPrefixes = false;
   bool MatchFullLines = false;
   bool IgnoreCase = false;
   bool IsDefaultCheckPrefix = false;
diff --git a/llvm/lib/FileCheck/FileCheck.cpp b/llvm/lib/FileCheck/FileCheck.cpp
--- a/llvm/lib/FileCheck/FileCheck.cpp
+++ b/llvm/lib/FileCheck/FileCheck.cpp
@@ -22,6 +22,7 @@
 #include "llvm/Support/FormatVariadic.h"
 #include <cstdint>
 #include <list>
+#include <set>
 #include <tuple>
 #include <utility>
 
@@ -1825,8 +1826,10 @@
   // found.
   unsigned LineNumber = 1;
 
-  bool FoundUsedCheckPrefix = false;
-  while (1) {
+  std::set<StringRef> PrefixesNotFound(Req.CheckPrefixes.begin(),
+                                       Req.CheckPrefixes.end());
+  const size_t DistinctPrefixes = PrefixesNotFound.size();
+  while (true) {
     Check::FileCheckType CheckTy;
 
     // See if a prefix occurs in the memory buffer.
@@ -1837,7 +1840,7 @@
     if (UsedPrefix.empty())
       break;
     if (CheckTy != Check::CheckComment)
-      FoundUsedCheckPrefix = true;
+      PrefixesNotFound.erase(UsedPrefix);
 
     assert(UsedPrefix.data() == Buffer.data() &&
            "Failed to move Buffer's start forward, or pointed prefix outside "
@@ -1930,14 +1933,19 @@
 
   // When there are no used prefixes we report an error except in the case that
   // no prefix is specified explicitly but -implicit-check-not is specified.
-  if (!FoundUsedCheckPrefix &&
+  const bool NoPrefixesFound = PrefixesNotFound.size() == DistinctPrefixes;
+  const bool SomePrefixesUnexpectedlyNotUsed =
+      !Req.AllowUnusedPrefixes && !PrefixesNotFound.empty();
+  if ((NoPrefixesFound || SomePrefixesUnexpectedlyNotUsed) &&
       (ImplicitNegativeChecks.empty() || !Req.IsDefaultCheckPrefix)) {
     errs() << "error: no check strings found with prefix"
-           << (Req.CheckPrefixes.size() > 1 ? "es " : " ");
-    for (size_t I = 0, E = Req.CheckPrefixes.size(); I != E; ++I) {
-      if (I != 0)
+           << (PrefixesNotFound.size() > 1 ? "es " : " ");
+    bool First = true;
+    for (StringRef MissingPrefix : PrefixesNotFound) {
+      if (!First)
         errs() << ", ";
-      errs() << "\'" << Req.CheckPrefixes[I] << ":'";
+      errs() << "\'" << MissingPrefix << ":'";
+      First = false;
     }
     errs() << '\n';
     return true;
diff --git a/llvm/test/FileCheck/Inputs/one-check.txt b/llvm/test/FileCheck/Inputs/one-check.txt
new file mode 100644
--- /dev/null
+++ b/llvm/test/FileCheck/Inputs/one-check.txt
@@ -0,0 +1,2 @@
+hello
+; P1: hello
\ No newline at end of file
diff --git a/llvm/test/FileCheck/allow-unused-prefixes.txt b/llvm/test/FileCheck/allow-unused-prefixes.txt
new file mode 100644
--- /dev/null
+++ b/llvm/test/FileCheck/allow-unused-prefixes.txt
@@ -0,0 +1,10 @@
+; RUN: not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-ONE %s
+; RUN: not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2,P3 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-MORE %s
+; RUN: FileCheck --allow-unused-prefixes=true  --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 
+
+; Note: the default will be changed to 'false', at which time this run line
+; should be changed accordingly.
+; RUN: FileCheck --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 
+
+; MISSING-ONE: error: no check strings found with prefix 'P2:' 
+; MISSING-MORE: error: no check strings found with prefixes 'P2:', 'P3:' 
\ No newline at end of file
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
@@ -77,6 +77,10 @@
     cl::desc("Allow the input file to be empty. This is useful when making\n"
              "checks that some error message does not occur, for example."));
 
+static cl::opt<bool> AllowUnusedPrefixes(
+    "allow-unused-prefixes", cl::init(true),
+    cl::desc("Allow prefixes to be specified but not appear in the test."));
+
 static cl::opt<bool> MatchFullLines(
     "match-full-lines", cl::init(false),
     cl::desc("Require all positive matches to cover an entire input line.\n"
@@ -771,6 +775,7 @@
     return 2;
 
   Req.AllowEmptyInput = AllowEmptyInput;
+  Req.AllowUnusedPrefixes = AllowUnusedPrefixes;
   Req.EnableVarScope = EnableVarScope;
   Req.AllowDeprecatedDagOverlap = AllowDeprecatedDagOverlap;
   Req.Verbose = Verbose;