diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index b0fd1d77a2d66..c8c5b0880819a 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -304,9 +304,14 @@ std::string llvm::computeLTOCacheKey(
     }
   };
 
-  // Include the hash for the linkage type to reflect internalization and weak
-  // resolution, and collect any used type identifier resolutions.
-  for (auto &GS : DefinedGlobals) {
+  // Sort the defined globals by GUID to be independent of the insertion order,
+  // which may depend on the order that modules are added.
+  SmallVector<std::pair<GlobalValue::GUID, GlobalValueSummary *>>
+      SortedDefinedGlobals(DefinedGlobals.begin(), DefinedGlobals.end());
+  llvm::sort(SortedDefinedGlobals, llvm::less_first());
+  for (auto &GS : SortedDefinedGlobals) {
+    // Include the hash for the linkage type to reflect internalization and weak
+    // resolution, and collect any used type identifier resolutions.
     GlobalValue::LinkageTypes Linkage = GS.second->linkage();
     Hasher.update(
         ArrayRef<uint8_t>((const uint8_t *)&Linkage, sizeof(Linkage)));
diff --git a/llvm/test/ThinLTO/X86/Inputs/cache-defined-globals-order.ll b/llvm/test/ThinLTO/X86/Inputs/cache-defined-globals-order.ll
new file mode 100644
index 0000000000000..5a527c9bae924
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/cache-defined-globals-order.ll
@@ -0,0 +1,6 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define linkonce_odr void @shared29() {
+  ret void
+}
diff --git a/llvm/test/ThinLTO/X86/cache-defined-globals-order.ll b/llvm/test/ThinLTO/X86/cache-defined-globals-order.ll
new file mode 100644
index 0000000000000..84f71f20f9e6d
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/cache-defined-globals-order.ll
@@ -0,0 +1,27 @@
+; RUN: rm -rf %t && mkdir -p %t
+; RUN: opt -module-hash -module-summary %s -o %t/t.bc
+; RUN: opt -module-hash -module-summary %S/Inputs/cache-defined-globals-order.ll -o %t/a.bc
+
+; Tests that the LTO cache key is insensitive to the order of the modules.
+; The linkonce_odr function @shared29 is defined in both t.bc and a.bc, so
+; it gets a different position in the combined index depending on which
+; module is processed first, which results in a different insertion order
+; for DefinedGlobals.
+
+; RUN: llvm-lto2 run -cache-dir %t/cache -o %t.o %t/t.bc %t/a.bc -r=%t/t.bc,main,plx -r=%t/t.bc,shared29,plx -r=%t/a.bc,shared29,lx
+; RUN: ls %t/cache | count 2
+
+; RUN: llvm-lto2 run -cache-dir %t/cache -o %t.o %t/a.bc %t/t.bc -r=%t/t.bc,main,plx -r=%t/t.bc,shared29,plx -r=%t/a.bc,shared29,lx
+; RUN: ls %t/cache | count 2
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @main() {
+  call void @shared29()
+  ret void
+}
+
+define linkonce_odr void @shared29() {
+  ret void
+}