diff --git a/lib/dusbextreme.d b/lib/dusbextreme.d
index 47cb27b..820ae25 100644
--- a/lib/dusbextreme.d
+++ b/lib/dusbextreme.d
@@ -48,3 +48,14 @@ extern(C) UsbExtremeVersion get_version(uint8_t usbExtremeVersion) {
         }
     }
 }
+
+extern(C) int oue_num_headers(int *num_headers, immutable(void) *headers, size_t headerslen) {
+    auto headers_nlen = cast(int) (headerslen / USBEXTREME_HEADER_SIZE);
+
+    if (!is_oue(headers, headerslen)) {
+        return -1;
+    }
+
+    *num_headers = headers_nlen;
+    return headers_nlen;
+}
diff --git a/lib/usbextreme.c b/lib/usbextreme.c
index cf631d6..3d75e8f 100644
--- a/lib/usbextreme.c
+++ b/lib/usbextreme.c
@@ -12,17 +12,6 @@ int oue_point_headers(usb_extreme_base **headers, void *raw_headers, size_t head
     return headers_nlen;
 }
 
-int oue_num_headers(int *num_headers, const void *headers, size_t headerslen) {
-    int headers_nlen = (int) (headerslen / USBEXTREME_HEADER_SIZE);
-
-    if (!is_oue(headers, headerslen)) {
-        return -1;
-    }
-
-    *num_headers = headers_nlen;
-    return headers_nlen;
-}
-
 int oue_version(usb_extreme_versions *version, const void *headers, size_t headerslen) {
     const usb_extreme_v1 *headers_oeu = headers;
     int headers_nlen = (int) (headerslen / USBEXTREME_HEADER_SIZE);