diff --git a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
--- a/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
@@ -1295,7 +1295,13 @@
       std::optional<APInt> FalseDiff =
           getConstantOffset(SelectA->getFalseValue(), SelectB->getFalseValue(),
                             ContextInst, Depth);
-      if (TrueDiff == FalseDiff)
+      // A bit unclear how we can get TrueDiff and FalseDiff with different bit
+      // widths, since the bit width returned by getConstantOffset is determined
+      // by the datatype of the pointer, and both sides of the `select` should
+      // have the same datatype.  But we seem to be hitting this in practice.
+      if (FalseDiff.has_value() &&
+          TrueDiff->getBitWidth() == FalseDiff->getBitWidth() &&
+          TrueDiff == FalseDiff)
         return TrueDiff;
     }
   }