diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6bc2ece..9476ce8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,7 +32,7 @@ set(SOURCE
   ${LAYER_SELECTOR_SOURCES}
 )
 
-add_compile_options(-Wall)
+add_compile_options(-Wall -Wold-style-declaration)
 
 add_executable(${PROJECT_NAME} ${SOURCE} ${CMAKE_CURRENT_BINARY_DIR}/resources/resources.c)
 add_dependencies(${PROJECT_NAME} glib-resources)
diff --git a/main.c b/main.c
index b0b8471..3e27d89 100644
--- a/main.c
+++ b/main.c
@@ -117,7 +117,7 @@ static void app_about(GSimpleAction *action, GVariant *parameter, gpointer user_
 /**
  * @brief Contains the application menu entries
  */
-const static GActionEntry app_actions[] = {
+static const GActionEntry app_actions[] = {
 	{"quit", app_quit, NULL, NULL, NULL, {0}},
 	{"about", app_about, NULL, NULL, NULL, {0}}
 };
diff --git a/widgets/conv-settings-dialog.c b/widgets/conv-settings-dialog.c
index c09400e..538f4dc 100644
--- a/widgets/conv-settings-dialog.c
+++ b/widgets/conv-settings-dialog.c
@@ -183,10 +183,10 @@ static double convert_number_to_engineering(double input, const char **out_prefi
 	const char *selected_prefix = NULL;
 	double return_val = 0.0;
 	int idx;
-	const static char * prefixes[] = {"y", "z", "a", "f", "p", "n", "u", "m", "c", "d", /* < 1 */
+	static const char * prefixes[] = {"y", "z", "a", "f", "p", "n", "u", "m", "c", "d", /* < 1 */
 				 "", /* 1 */
 				 "h", "k", "M", "G", "T", "P", "E", "Z", "Y"}; /* > 1 */
-	const static double scale[] = {1E-24, 1E-21, 1E-18, 1E-15, 1E-12, 1E-9, 1E-6, 1E-3, 1E-2, 1E-1,
+	static const double scale[] = {1E-24, 1E-21, 1E-18, 1E-15, 1E-12, 1E-9, 1E-6, 1E-3, 1E-2, 1E-1,
 					1,
 					1E2, 1E3, 1E6, 1E9, 1E12, 1E15, 1E18, 1E21, 1E24};
 	const int prefix_count = (int)(sizeof(prefixes)/sizeof(char *));