diff --git a/src/impl/constexpr.inc b/src/impl/constexpr.inl
similarity index 100%
rename from src/impl/constexpr.inc
rename to src/impl/constexpr.inl
diff --git a/src/impl/inline.inc b/src/impl/inline.inl
similarity index 100%
rename from src/impl/inline.inc
rename to src/impl/inline.inl
diff --git a/src/impl/sine.inc b/src/impl/sine.inl
similarity index 100%
rename from src/impl/sine.inc
rename to src/impl/sine.inl
diff --git a/src/impl/value.inc b/src/impl/value.inl
similarity index 99%
rename from src/impl/value.inc
rename to src/impl/value.inl
index f3a63a8..4ebc661 100644
--- a/src/impl/value.inc
+++ b/src/impl/value.inl
@@ -1,6 +1,6 @@
 #pragma once
 
-#include "sine.inc"
+#include "sine.inl"
 
 namespace md5::value {
 
diff --git a/src/md5.h b/src/md5.h
index fc8d707..bb098ac 100644
--- a/src/md5.h
+++ b/src/md5.h
@@ -12,8 +12,8 @@ static_assert(__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__,
 
 #define MD5_EXPORT __attribute__ ((visibility ("default")))
 
-#include "impl/value.inc"
-#include "impl/constexpr.inc"
+#include "impl/value.inl"
+#include "impl/constexpr.inl"
 
 namespace md5 {
 
@@ -70,4 +70,4 @@ private:
 
 } // namespace md5
 
-#include "impl/inline.inc"
+#include "impl/inline.inl"