diff --git a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
index 352a1b331001a..1976baff783fa 100644
--- a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
@@ -1048,7 +1048,8 @@ bool InferAddressSpacesImpl::updateAddressSpace(
   } else {
     // Otherwise, infer the address space from its pointer operands.
     SmallVector<Constant *, 2> ConstantPtrOps;
-    for (Value *PtrOperand : getPointerOperands(V, *DL, TTI)) {
+    SmallVector<Value *, 2> PtrOps = getPointerOperands(V, *DL, TTI);
+    for (Value *PtrOperand : PtrOps) {
       auto I = InferredAddrSpace.find(PtrOperand);
       unsigned OperandAS;
       if (I == InferredAddrSpace.end()) {
@@ -1079,12 +1080,18 @@ bool InferAddressSpacesImpl::updateAddressSpace(
       if (NewAS == FlatAddrSpace)
         break;
     }
+
     if (NewAS != FlatAddrSpace && NewAS != UninitializedAddressSpace) {
       if (any_of(ConstantPtrOps, [=](Constant *C) {
             return !isSafeToCastConstAddrSpace(C, NewAS);
           }))
         NewAS = FlatAddrSpace;
     }
+
+    // operator(flat const, flat const, ...) -> flat
+    if (NewAS == UninitializedAddressSpace &&
+        PtrOps.size() == ConstantPtrOps.size())
+      NewAS = FlatAddrSpace;
   }
 
   unsigned OldAS = InferredAddrSpace.lookup(&V);
diff --git a/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll b/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll
new file mode 100644
index 0000000000000..af48db7773c42
--- /dev/null
+++ b/llvm/test/Transforms/InferAddressSpaces/NVPTX/nullptr.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=infer-address-spaces %s | FileCheck %s
+
+target triple = "nvptx64-unknown-nvidiacl"
+
+define ptr @pr171890(i1 %c) {
+; CHECK-LABEL: define ptr @pr171890(
+; CHECK-SAME: i1 [[C:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[STACK:%.*]] = alloca i16, align 2
+; CHECK-NEXT:    [[TMP0:%.*]] = addrspacecast ptr [[STACK]] to ptr addrspace(5)
+; CHECK-NEXT:    [[TMP1:%.*]] = addrspacecast ptr addrspace(5) [[TMP0]] to ptr
+; CHECK-NEXT:    [[CONST:%.*]] = getelementptr i8, ptr null, i64 1
+; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[C]], ptr [[TMP1]], ptr [[CONST]]
+; CHECK-NEXT:    ret ptr [[SEL]]
+;
+entry:
+  %stack = alloca i16, align 2
+  %const = getelementptr i8, ptr null, i64 1
+  %sel = select i1 %c, ptr %stack, ptr %const
+  ret ptr %sel
+}