diff --git a/contrib/zopfli/CMakeLists.txt b/contrib/zopfli/CMakeLists.txt
index 4de454d..59b1b27 100644
--- a/contrib/zopfli/CMakeLists.txt
+++ b/contrib/zopfli/CMakeLists.txt
@@ -45,9 +45,9 @@ add_sapi_library(
     ZopfliGzipCompress
 
   INPUTS
-    ${zopfli_SOURCE_DIR}/src/zopfli/deflate.h
-    ${zopfli_SOURCE_DIR}/src/zopfli/gzip_container.h
-    ${zopfli_SOURCE_DIR}/src/zopfli/zlib_container.h
+    "${zopfli_SOURCE_DIR}/src/zopfli/deflate.h"
+    "${zopfli_SOURCE_DIR}/src/zopfli/gzip_container.h"
+    "${zopfli_SOURCE_DIR}/src/zopfli/zlib_container.h"
 
   LIBRARY Zopfli::libzopfli
   LIBRARY_NAME Zopfli
diff --git a/contrib/zstd/CMakeLists.txt b/contrib/zstd/CMakeLists.txt
index bae244f..eab5b02 100644
--- a/contrib/zstd/CMakeLists.txt
+++ b/contrib/zstd/CMakeLists.txt
@@ -71,7 +71,7 @@ add_sapi_library(
     ZSTD_getFrameContentSize
 
   INPUTS
-    ${libzstd_INCLUDE_DIR}/zstd.h
+    "${libzstd_INCLUDE_DIR}/zstd.h"
 
   LIBRARY libzstd_static
   LIBRARY_NAME Zstd