diff --git a/projects/openttd.vcproj b/projects/openttd.vcproj
index 6500d1d9ff..0a7e6bb26d 100644
--- a/projects/openttd.vcproj
+++ b/projects/openttd.vcproj
@@ -402,6 +402,9 @@
 			<File
 				RelativePath=".\..\src\articulated_vehicles.h">
 			</File>
+			<File
+				RelativePath=".\..\src\autoslope.h">
+			</File>
 			<File
 				RelativePath=".\..\src\aystar.h">
 			</File>
diff --git a/projects/openttd_vs80.vcproj b/projects/openttd_vs80.vcproj
index 2d3e49bc7a..2a79f1c916 100644
--- a/projects/openttd_vs80.vcproj
+++ b/projects/openttd_vs80.vcproj
@@ -767,6 +767,10 @@
 				RelativePath=".\..\src\articulated_vehicles.h"
 				>
 			</File>
+			<File
+				RelativePath=".\..\src\autoslope.h"
+				>
+			</File>
 			<File
 				RelativePath=".\..\src\aystar.h"
 				>