diff --git a/mlir/CMakeLists.txt b/mlir/CMakeLists.txt
--- a/mlir/CMakeLists.txt
+++ b/mlir/CMakeLists.txt
@@ -89,6 +89,7 @@
     DESTINATION include
     COMPONENT mlir-headers
     FILES_MATCHING
+    PATTERN "*.def"
     PATTERN "*.h"
     PATTERN "*.inc"
     PATTERN "*.td"