Index: clang/lib/CrossTU/CrossTranslationUnit.cpp
===================================================================
--- clang/lib/CrossTU/CrossTranslationUnit.cpp
+++ clang/lib/CrossTU/CrossTranslationUnit.cpp
@@ -157,7 +157,7 @@
   unsigned LineNo = 1;
   while (std::getline(ExternalMapFile, Line)) {
     StringRef LineRef{Line};
-    const size_t Delimiter = LineRef.find(' ');
+    const size_t Delimiter = LineRef.rfind(' ');
     if (Delimiter > 0 && Delimiter != std::string::npos) {
       StringRef LookupName = LineRef.substr(0, Delimiter);
 
Index: clang/test/Analysis/Inputs/ctu-lookup-name-with-space.cpp
===================================================================
--- /dev/null
+++ clang/test/Analysis/Inputs/ctu-lookup-name-with-space.cpp
@@ -0,0 +1,14 @@
+void f(int (*)(char));
+void f(bool (*)(char));
+
+struct G {
+  G() {
+    // CHECK-NOT: error: multiple definitions are found for the same key in index
+    f([](char) -> int { return 42; });
+    f([](char) -> bool { return true; });
+  }
+};
+
+int importee(int X) {
+  return 1 / X;
+}
Index: clang/test/Analysis/ctu-lookup-name-with-space.cpp
===================================================================
--- /dev/null
+++ clang/test/Analysis/ctu-lookup-name-with-space.cpp
@@ -0,0 +1,29 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+
+// RUN: cp %s %t/trigger.cpp
+// RUN: cp %S/Inputs/ctu-lookup-name-with-space.cpp %t/importee.cpp
+// RUN: echo '"%t/importee.cpp" : ["g++", "-c", "%t/importee.cpp"]' > %t/invocations.yaml
+// RUN: echo '[{"directory": "%t", "command": "g++ -c %t/importee.cpp", "file": "%t/importee.cpp"}, {"directory": "%t", "command": "g++ -c %t/trigger.cpp", "file": "%t/trigger.cpp"}]' > %t/compile_commands.json
+
+// RUN: %clang_extdef_map -p %t %t/importee.cpp > %t/externalDefMap.txt
+
+// RUN: cd %t && %clang_cc1 -fsyntax-only -analyze \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-config experimental-enable-naive-ctu-analysis=true \
+// RUN:   -analyzer-config ctu-dir=. \
+// RUN:   -analyzer-config ctu-invocation-list=invocations.yaml \
+// RUN:   trigger.cpp 2>&1 | FileCheck importee.cpp
+
+// RUN: cd %t && %clang_cc1 -fsyntax-only -analyze \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-config experimental-enable-naive-ctu-analysis=true \
+// RUN:   -analyzer-config ctu-dir=. \
+// RUN:   -analyzer-config ctu-invocation-list=invocations.yaml \
+// RUN:   -verify trigger.cpp
+
+int importee(int);
+
+void trigger() {
+  importee(0); // expected-warning@importee.cpp:13 {{Division by zero}}
+}