diff --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index c61531c5141a9..4026022caa079 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -1507,8 +1507,8 @@ void AtomicExpand::expandAtomicLoadToLibcall(LoadInst *I) {
   bool expanded = expandAtomicOpToLibcall(
       I, Size, I->getAlign(), I->getPointerOperand(), nullptr, nullptr,
       I->getOrdering(), AtomicOrdering::NotAtomic, Libcalls);
-  (void)expanded;
-  assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor Load");
+  if (!expanded)
+    report_fatal_error("expandAtomicOpToLibcall shouldn't fail for Load");
 }
 
 void AtomicExpand::expandAtomicStoreToLibcall(StoreInst *I) {
@@ -1520,8 +1520,8 @@ void AtomicExpand::expandAtomicStoreToLibcall(StoreInst *I) {
   bool expanded = expandAtomicOpToLibcall(
       I, Size, I->getAlign(), I->getPointerOperand(), I->getValueOperand(),
       nullptr, I->getOrdering(), AtomicOrdering::NotAtomic, Libcalls);
-  (void)expanded;
-  assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor Store");
+  if (!expanded)
+    report_fatal_error("expandAtomicOpToLibcall shouldn't fail for Store");
 }
 
 void AtomicExpand::expandAtomicCASToLibcall(AtomicCmpXchgInst *I) {
@@ -1535,8 +1535,8 @@ void AtomicExpand::expandAtomicCASToLibcall(AtomicCmpXchgInst *I) {
       I, Size, I->getAlign(), I->getPointerOperand(), I->getNewValOperand(),
       I->getCompareOperand(), I->getSuccessOrdering(), I->getFailureOrdering(),
       Libcalls);
-  (void)expanded;
-  assert(expanded && "expandAtomicOpToLibcall shouldn't fail tor CAS");
+  if (!expanded)
+    report_fatal_error("expandAtomicOpToLibcall shouldn't fail for CAS");
 }
 
 static ArrayRef<RTLIB::Libcall> GetRMWLibcall(AtomicRMWInst::BinOp Op) {
@@ -1685,6 +1685,11 @@ bool AtomicExpand::expandAtomicOpToLibcall(
     return false;
   }
 
+  if (!TLI->getLibcallName(RTLibType)) {
+    // This target does not implement the requested atomic libcall so give up.
+    return false;
+  }
+
   // Build up the function call. There's two kinds. First, the sized
   // variants.  These calls are going to be one of the following (with
   // N=1,2,4,8,16):
diff --git a/llvm/test/Transforms/AtomicExpand/AMDGPU/unaligned-atomic.ll b/llvm/test/Transforms/AtomicExpand/AMDGPU/unaligned-atomic.ll
index 3d21e15100153..56db423af6f50 100644
--- a/llvm/test/Transforms/AtomicExpand/AMDGPU/unaligned-atomic.ll
+++ b/llvm/test/Transforms/AtomicExpand/AMDGPU/unaligned-atomic.ll
@@ -1,8 +1,6 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -atomic-expand %s | FileCheck -check-prefix=GCN %s
-
-; FIXME: This should not introduce a libcall, much less one to an
-; anonymous function.
+; RUN: not --crash opt -S -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -atomic-expand %s 2>&1 | FileCheck %s
+; The AtomicExpand pass cannot handle missing libcalls (yet) so reports a fatal error.
+; CHECK: LLVM ERROR: expandAtomicOpToLibcall shouldn't fail for Load
 
 define i32 @atomic_load_global_align1(i32 addrspace(1)* %ptr) {
 ; GCN-LABEL: @atomic_load_global_align1(