diff --git a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
--- a/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
+++ b/mlir/lib/Dialect/MemRef/IR/MemRefOps.cpp
@@ -284,7 +284,10 @@
     // Check to see if any dimensions operands are constants.  If so, we can
     // substitute and drop them.
     if (llvm::none_of(alloc.getDynamicSizes(), [](Value operand) {
-          return matchPattern(operand, matchConstantIndex());
+          APInt constSizeArg;
+          if (!matchPattern(operand, m_ConstantInt(&constSizeArg)))
+            return false;
+          return constSizeArg.isNonNegative();
         }))
       return failure();
 
@@ -305,12 +308,13 @@
         continue;
       }
       auto dynamicSize = alloc.getDynamicSizes()[dynamicDimPos];
-      auto *defOp = dynamicSize.getDefiningOp();
-      if (auto constantIndexOp =
-              dyn_cast_or_null<arith::ConstantIndexOp>(defOp)) {
+      APInt constSizeArg;
+      if (matchPattern(dynamicSize, m_ConstantInt(&constSizeArg))
+          && constSizeArg.isNonNegative()) {
         // Dynamic shape dimension will be folded.
-        newShapeConstants.push_back(constantIndexOp.value());
-      } else {
+        newShapeConstants.push_back(constSizeArg.getZExtValue());
+        }
+      else {
         // Dynamic shape dimension not folded; copy dynamicSize from old memref.
         newShapeConstants.push_back(ShapedType::kDynamic);
         dynamicSizes.push_back(dynamicSize);
diff --git a/mlir/test/Dialect/MemRef/canonicalize.mlir b/mlir/test/Dialect/MemRef/canonicalize.mlir
--- a/mlir/test/Dialect/MemRef/canonicalize.mlir
+++ b/mlir/test/Dialect/MemRef/canonicalize.mlir
@@ -928,3 +928,15 @@
   %1 = memref.memory_space_cast %0 : memref<?xf32, 1> to memref<?xf32, 2>
   return %1 : memref<?xf32, 2>
 }
+
+// -----
+
+// CHECK-lABEL: func @ub_negative_alloc_size
+func.func private @ub_negative_alloc_size() -> memref<?x?x?xi1> {
+  %idx1 = index.constant 1
+  %c-2 = arith.constant -2 : index
+  %c15 = arith.constant 15 : index
+// CHECK:   %[[ALLOC:.*]] = memref.alloc(%c-2) : memref<15x?x1xi1>
+  %alloc = memref.alloc(%c15, %c-2, %idx1) : memref<?x?x?xi1>
+  return %alloc : memref<?x?x?xi1>
+}