diff --git a/CMakeLists.txt b/CMakeLists.txt
index 002a3e7e9..fddeeddfd 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,8 @@
 cmake_minimum_required(VERSION 3.5)
 
+# needed for lto to work for some reason
+cmake_policy(SET CMP0069 NEW)
+
 if(${PROJECT_SOURCE_DIR} MATCHES ${PROJECT_BINARY_DIR})
 	message(FATAL_ERROR "In-source builds will bring you a world of pain. Please make a separate directory to invoke CMake from.")
 endif()
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 2de66a5af..dc456905a 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -54,7 +54,7 @@ set(SRB2_CORE_SOURCES
 	string.c
 	tables.c
 	v_video.c
-	w_wad.cpp
+	w_wad.c
 	y_inter.c
 	z_zone.cpp
 )
@@ -518,7 +518,7 @@ if(${SRB2_CONFIG_HWRENDER})
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_batching.c
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_shaders.c
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_bsp.c
-		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_cache.cpp
+		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_cache.c
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_clip.c
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_draw.c
 		${CMAKE_CURRENT_SOURCE_DIR}/hardware/hw_main.cpp