diff --git a/mlir/include/mlir/IR/StandardTypes.h b/mlir/include/mlir/IR/StandardTypes.h
--- a/mlir/include/mlir/IR/StandardTypes.h
+++ b/mlir/include/mlir/IR/StandardTypes.h
@@ -416,8 +416,8 @@
 
 /// MemRef types represent a region of memory that have a shape with a fixed
 /// number of dimensions. Each shape element can be a non-negative integer or
-/// unknown (represented by any negative integer). MemRef types also have an
-/// affine map composition, represented as an array AffineMap pointers.
+/// unknown (represented by -1). MemRef types also have an affine map
+/// composition, represented as an array AffineMap pointers.
 class MemRefType : public Type::TypeBase<MemRefType, BaseMemRefType,
                                          detail::MemRefTypeStorage> {
 public: