diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index fe74c5f7d4b3..a41ee6074153 100644
--- a/lib/LTO/LTO.cpp
+++ b/lib/LTO/LTO.cpp
@@ -84,6 +84,18 @@ static void computeCacheKey(
     Data[3] = I >> 24;
     Hasher.update(ArrayRef<uint8_t>{Data, 4});
   };
+  auto AddUint64 = [&](uint64_t I) {
+    uint8_t Data[8];
+    Data[0] = I;
+    Data[1] = I >> 8;
+    Data[2] = I >> 16;
+    Data[3] = I >> 24;
+    Data[4] = I >> 32;
+    Data[5] = I >> 40;
+    Data[6] = I >> 48;
+    Data[7] = I >> 56;
+    Hasher.update(ArrayRef<uint8_t>{Data, 8});
+  };
   AddString(Conf.CPU);
   // FIXME: Hash more of Options. For now all clients initialize Options from
   // command-line flags (which is unsupported in production), but may set
@@ -112,10 +124,16 @@ static void computeCacheKey(
     // The export list can impact the internalization, be conservative here
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&F, sizeof(F)));
 
-  // Include the hash for every module we import functions from
+  // Include the hash for every module we import functions from. The set of
+  // imported symbols for each module may affect code generation and is
+  // sensitive to link order, so include that as well.
   for (auto &Entry : ImportList) {
     auto ModHash = Index.getModuleHash(Entry.first());
     Hasher.update(ArrayRef<uint8_t>((uint8_t *)&ModHash[0], sizeof(ModHash)));
+
+    AddUint64(Entry.second.size());
+    for (auto &Fn : Entry.second)
+      AddUint64(Fn.first);
   }
 
   // Include the hash for the resolved ODR.
diff --git a/test/ThinLTO/X86/Inputs/cache-import-lists1.ll b/test/ThinLTO/X86/Inputs/cache-import-lists1.ll
new file mode 100644
index 000000000000..58bfb39f9ee1
--- /dev/null
+++ b/test/ThinLTO/X86/Inputs/cache-import-lists1.ll
@@ -0,0 +1,11 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f1() {
+  call void @linkonce_odr()
+  ret void
+}
+
+define linkonce_odr void @linkonce_odr() {
+  ret void
+}
diff --git a/test/ThinLTO/X86/Inputs/cache-import-lists2.ll b/test/ThinLTO/X86/Inputs/cache-import-lists2.ll
new file mode 100644
index 000000000000..899bbaea13d6
--- /dev/null
+++ b/test/ThinLTO/X86/Inputs/cache-import-lists2.ll
@@ -0,0 +1,11 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @f2() {
+  call void @linkonce_odr()
+  ret void
+}
+
+define linkonce_odr void @linkonce_odr() {
+  ret void
+}
diff --git a/test/ThinLTO/X86/cache-import-lists.ll b/test/ThinLTO/X86/cache-import-lists.ll
new file mode 100644
index 000000000000..6ec5dba10893
--- /dev/null
+++ b/test/ThinLTO/X86/cache-import-lists.ll
@@ -0,0 +1,24 @@
+; RUN: opt -module-hash -module-summary %s -o %t.bc
+; RUN: opt -module-hash -module-summary %S/Inputs/cache-import-lists1.ll -o %t1.bc
+; RUN: opt -module-hash -module-summary %S/Inputs/cache-import-lists2.ll -o %t2.bc
+
+; Tests that the hash for t is sensitive to the set of imported functions
+; for each module, which in this case depends on the link order (the function
+; linkonce_odr will be imported from either t1 or t2, whichever comes first).
+
+; RUN: rm -rf %t.cache
+; RUN: llvm-lto2 -cache-dir %t.cache -o %t.o %t.bc %t1.bc %t2.bc -r=%t.bc,main,plx -r=%t.bc,f1,lx -r=%t.bc,f2,lx -r=%t1.bc,f1,plx -r=%t1.bc,linkonce_odr,plx -r=%t2.bc,f2,plx -r=%t2.bc,linkonce_odr,lx
+; RUN: llvm-lto2 -cache-dir %t.cache -o %t.o %t.bc %t2.bc %t1.bc -r=%t.bc,main,plx -r=%t.bc,f1,lx -r=%t.bc,f2,lx -r=%t2.bc,f2,plx -r=%t2.bc,linkonce_odr,plx -r=%t1.bc,f1,plx -r=%t1.bc,linkonce_odr,lx
+; RUN: ls %t.cache | count 6
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @main() {
+  call void @f1()
+  call void @f2()
+  ret void
+}
+
+declare void @f1()
+declare void @f2()