diff --git a/include/splinepy/proximity/slsqp/slsqp.hpp b/include/splinepy/proximity/slsqp/slsqp.h
similarity index 100%
rename from include/splinepy/proximity/slsqp/slsqp.hpp
rename to include/splinepy/proximity/slsqp/slsqp.h
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d2563cbf6..6a8a326db 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -119,6 +119,12 @@ install(
   FILES_MATCHING
   PATTERN "*.hpp")
 
+install(
+  DIRECTORY "${PROJECT_SOURCE_DIR}/include/splinepy"
+  DESTINATION ${incl_dest} # target directory
+  FILES_MATCHING
+  PATTERN "*.h")
+
 # inline files - keep tree
 install(
   DIRECTORY "${PROJECT_SOURCE_DIR}/include/splinepy"
diff --git a/src/proximity/slsqp/slsqp.c b/src/proximity/slsqp/slsqp.c
index 3c853d31b..68b8d5db1 100644
--- a/src/proximity/slsqp/slsqp.c
+++ b/src/proximity/slsqp/slsqp.c
@@ -1,4 +1,4 @@
-#include "splinepy/proximity/slsqp/slsqp.hpp"
+#include "splinepy/proximity/slsqp/slsqp.h"
 
 #ifdef __cplusplus
 #include <cmath>