diff --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -36,12 +36,14 @@
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Value.h"
 #include "llvm/IR/NoFolder.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/IPO/ArgumentPromotion.h"
 #include "llvm/Transforms/Utils/Local.h"
@@ -6331,7 +6333,8 @@
       continue;
 
     if (Value *Align = getAllocAlignment(AI.CB, TLI)) {
-      if (!getAPInt(A, *this, *Align)) {
+      Optional<APInt> APAlign = getAPInt(A, *this, *Align);
+      if (!APAlign) {
         // Can't generate an alloca which respects the required alignment
         // on the allocation.
         LLVM_DEBUG(dbgs() << "[H2S] Unknown allocation alignment: " << *AI.CB
@@ -6339,6 +6342,14 @@
         AI.Status = AllocationInfo::INVALID;
         Changed = ChangeStatus::CHANGED;
         continue;
+      } else {
+        uint64_t AlignInt = APAlign.getValue().getZExtValue();
+        if (AlignInt > llvm::Value::MaximumAlignment || !isPowerOf2_64(AlignInt)) {
+          LLVM_DEBUG(dbgs() << "[H2S] Invalid allocation alignment: " << AlignInt << "\n");
+          AI.Status = AllocationInfo::INVALID;
+          Changed = ChangeStatus::CHANGED;
+          continue;
+        }
       }
     }
 
diff --git a/llvm/test/Transforms/Attributor/heap_to_stack.ll b/llvm/test/Transforms/Attributor/heap_to_stack.ll
--- a/llvm/test/Transforms/Attributor/heap_to_stack.ll
+++ b/llvm/test/Transforms/Attributor/heap_to_stack.ll
@@ -218,6 +218,20 @@
   ret void
 }
 
+; leave alone a constant-but-invalid alignment
+define void @test3d(i8* %p) {
+; CHECK-LABEL: define {{[^@]+}}@test3d
+; CHECK-SAME; (i8* nocapture [[P:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = tail call noalias i8* @aligned_alloc(i64 allocalign noundef 33, i64 noundef 128)
+; CHECK:    tail call void @free(i8* noalias nocapture [[TMP1]])
+; CHECK-NEXT:    ret void
+;
+  %1 = tail call noalias i8* @aligned_alloc(i64 allocalign 33, i64 128)
+  tail call void @nofree_arg_only(i8* %1, i8* %p)
+  tail call void @free(i8* %1)
+  ret void
+}
+
 declare noalias i8* @calloc(i64, i64)
 
 define void @test0() {