diff --git a/include/swift/AST/SearchPathOptions.h b/include/swift/AST/SearchPathOptions.h
index 0122d13fba2cc..7cde0bc4c1521 100644
--- a/include/swift/AST/SearchPathOptions.h
+++ b/include/swift/AST/SearchPathOptions.h
@@ -499,7 +499,7 @@ class SearchPathOptions {
   bool SkipSDKImportPaths = false;
 
   /// Scanner Prefix Mapper.
-  std::vector<std::string> ScannerPrefixMapper;
+  std::vector<std::pair<std::string, std::string>> ScannerPrefixMapper;
 
   /// Verify resolved plugin is not changed.
   bool ResolvedPluginVerification = false;
diff --git a/lib/AST/ModuleDependencies.cpp b/lib/AST/ModuleDependencies.cpp
index f0c4435820444..127db04b25349 100644
--- a/lib/AST/ModuleDependencies.cpp
+++ b/lib/AST/ModuleDependencies.cpp
@@ -755,12 +755,8 @@ bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
   if (!ScannerPrefixMapper.empty()) {
     Mapper = std::make_unique<llvm::PrefixMapper>();
     SmallVector<llvm::MappedPrefix, 4> Prefixes;
-    if (auto E = llvm::MappedPrefix::transformJoined(ScannerPrefixMapper,
-                                                     Prefixes)) {
-      Instance.getDiags().diagnose(SourceLoc(), diag::error_prefix_mapping,
-                                   toString(std::move(E)));
-      return true;
-    }
+    llvm::MappedPrefix::transformPairs(ScannerPrefixMapper,
+                                       Prefixes);
     Mapper->addRange(Prefixes);
     Mapper->sort();
   }
diff --git a/lib/ClangImporter/ClangModuleDependencyScanner.cpp b/lib/ClangImporter/ClangModuleDependencyScanner.cpp
index 4e63580f3cce4..97396d6d05b12 100644
--- a/lib/ClangImporter/ClangModuleDependencyScanner.cpp
+++ b/lib/ClangImporter/ClangModuleDependencyScanner.cpp
@@ -40,8 +40,9 @@ using namespace clang::tooling::dependencies;
 static void addScannerPrefixMapperInvocationArguments(
     std::vector<std::string> &invocationArgStrs, ASTContext &ctx) {
   for (const auto &arg : ctx.SearchPathOpts.ScannerPrefixMapper) {
-    std::string prefixMapArg = "-fdepscan-prefix-map=" + arg;
-    invocationArgStrs.push_back(prefixMapArg);
+    invocationArgStrs.push_back("-fdepscan-prefix-map");
+    invocationArgStrs.push_back(arg.first);
+    invocationArgStrs.push_back(arg.second);
   }
 }
 
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 8726b222ee576..b1ee37ea2e10b 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -35,6 +35,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/PrefixMapper.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/VersionTuple.h"
 #include "llvm/Support/WithColor.h"
@@ -2473,7 +2474,11 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts, ArgList &Args,
     Opts.DeserializedPathRecoverer.addMapping(SplitMap.first, SplitMap.second);
   }
   for (StringRef Opt : Args.getAllArgValues(OPT_scanner_prefix_map)) {
-    Opts.ScannerPrefixMapper.push_back(Opt.str());
+    if (auto Mapping = llvm::MappedPrefix::getFromJoined(Opt)) {
+      Opts.ScannerPrefixMapper.push_back({Mapping->Old, Mapping->New});
+    } else {
+      Diags.diagnose(SourceLoc(), diag::error_prefix_mapping, Opt);
+    }
   }
 
   Opts.ResolvedPluginVerification |=