diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 9a0d69c6c1b0e..7e4b6ab3363ed 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -69,6 +69,8 @@ Potentially Breaking Changes
   call the member ``operator delete`` instead of the expected global
   delete operator. The old behavior is retained under ``-fclang-abi-compat=21``
   flag.
+- Clang warning suppressions file, ``--warning-suppression-mappings=``, now will
+  use the last matching entry instead of the longest one.
 
 C/C++ Language Potentially Breaking Changes
 -------------------------------------------
diff --git a/clang/docs/WarningSuppressionMappings.rst b/clang/docs/WarningSuppressionMappings.rst
index d96341ac6e563..d8af856f64ef0 100644
--- a/clang/docs/WarningSuppressionMappings.rst
+++ b/clang/docs/WarningSuppressionMappings.rst
@@ -63,7 +63,7 @@ Format
 Warning suppression mappings uses the same format as
 :doc:`SanitizerSpecialCaseList`.
 
-Sections describe which diagnostic group's behaviour to change, e.g.
+Sections describe which diagnostic group's behavior to change, e.g.
 ``[unused]``. When a diagnostic is matched by multiple sections, the latest
 section takes precedence.
 
@@ -76,7 +76,7 @@ Source files are matched against these globs either:
 - as paths relative to the current working directory
 - as absolute paths.
 
-When a source file matches multiple globs in a section, the longest one takes
+When a source file matches multiple globs in a section, the last one takes
 precedence.
 
 .. code-block:: bash
diff --git a/clang/include/clang/Basic/Diagnostic.h b/clang/include/clang/Basic/Diagnostic.h
index e540040ddc524..c6e931d0c9517 100644
--- a/clang/include/clang/Basic/Diagnostic.h
+++ b/clang/include/clang/Basic/Diagnostic.h
@@ -971,7 +971,7 @@ class DiagnosticsEngine : public RefCountedBase<DiagnosticsEngine> {
   /// diagnostics in specific files.
   /// Mapping file is expected to be a special case list with sections denoting
   /// diagnostic groups and `src` entries for globs to suppress. `emit` category
-  /// can be used to disable suppression. Longest glob that matches a filepath
+  /// can be used to disable suppression. The last glob that matches a filepath
   /// takes precedence. For example:
   ///   [unused]
   ///   src:clang/*
diff --git a/clang/lib/Basic/Diagnostic.cpp b/clang/lib/Basic/Diagnostic.cpp
index 8ecbd3c5a2cc4..e7373bf9eef27 100644
--- a/clang/lib/Basic/Diagnostic.cpp
+++ b/clang/lib/Basic/Diagnostic.cpp
@@ -587,15 +587,15 @@ bool WarningsSpecialCaseList::isDiagSuppressed(diag::kind DiagId,
 
   StringRef F = llvm::sys::path::remove_leading_dotslash(PLoc.getFilename());
 
-  StringRef LongestSup = DiagSection->getLongestMatch("src", F, "");
-  if (LongestSup.empty())
+  unsigned SuppressLineNo = DiagSection->getLastMatch("src", F, "");
+  if (!SuppressLineNo)
     return false;
 
-  StringRef LongestEmit = DiagSection->getLongestMatch("src", F, "emit");
-  if (LongestEmit.empty())
+  unsigned EmitLineNo = DiagSection->getLastMatch("src", F, "emit");
+  if (!EmitLineNo)
     return true;
 
-  return LongestSup.size() > LongestEmit.size();
+  return SuppressLineNo > EmitLineNo;
 }
 
 bool DiagnosticsEngine::isSuppressedViaMapping(diag::kind DiagId,
diff --git a/clang/unittests/Basic/DiagnosticTest.cpp b/clang/unittests/Basic/DiagnosticTest.cpp
index de090864e5095..5492146f40fa9 100644
--- a/clang/unittests/Basic/DiagnosticTest.cpp
+++ b/clang/unittests/Basic/DiagnosticTest.cpp
@@ -294,7 +294,7 @@ TEST_F(SuppressionMappingTest, EmitCategoryIsExcluded) {
                                             locForFile("foo.cpp")));
 }
 
-TEST_F(SuppressionMappingTest, LongestMatchWins) {
+TEST_F(SuppressionMappingTest, LastMatchWins) {
   llvm::StringLiteral SuppressionMappingFile = R"(
   [unused]
   src:*clang/*
@@ -327,10 +327,8 @@ TEST_F(SuppressionMappingTest, LongShortMatch) {
 
   EXPECT_TRUE(Diags.isSuppressedViaMapping(diag::warn_unused_function,
                                            locForFile("test/t1.cpp")));
-
-  // FIXME: This is confusing.
-  EXPECT_TRUE(Diags.isSuppressedViaMapping(diag::warn_unused_function,
-                                           locForFile("lld/test/t2.cpp")));
+  EXPECT_FALSE(Diags.isSuppressedViaMapping(diag::warn_unused_function,
+                                            locForFile("lld/test/t2.cpp")));
 }
 
 TEST_F(SuppressionMappingTest, ShortLongMatch) {