diff --git a/Makefile b/Makefile
index debf410..7688ec9 100644
--- a/Makefile
+++ b/Makefile
@@ -32,6 +32,10 @@ endef
 $(call pkgconf,QT5CORE,Qt5Core)
 $(call pkgconf,QT5WIDGETS,Qt5Widgets)
 
+CFLAGS   ?= -Wall -Wextra
+CXXFLAGS ?= -Wall -Wextra
+LDFLAGS  ?=
+
 # temporary workaround for broken cflags in kobo-toolchain Docker image:
 QT5CORE_CFLAGS    := $(shell echo "$(QT5CORE_CFLAGS)"    | sed 's:/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/:/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/:g')
 QT5WIDGETS_CFLAGS := $(shell echo "$(QT5WIDGETS_CFLAGS)" | sed 's:/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/:/toolchain/arm-nickel-linux-gnueabihf/arm-nickel-linux-gnueabihf/sysroot/:g')
diff --git a/src/menu.cc b/src/menu.cc
index 3b2db8f..f3aa991 100644
--- a/src/menu.cc
+++ b/src/menu.cc
@@ -55,6 +55,7 @@ extern "C" int nmi_menu_hook(void *libnickel, nmi_menu_entry_t *entries, size_t
     _entries = entries;
     _entries_n = entries_n;
 
+    NMI_RETURN_OK(0);
     #undef NMI_ERR_RET
 }
 
@@ -93,7 +94,7 @@ extern "C" MenuTextItem* _nmi_menu_hook(void* _this, QMenu* menu, QString const&
                 free(err);
                 return;
             }
-            NMI_LOG("Success!", err);
+            NMI_LOG("Success!");
         }));
     }
 
diff --git a/src/subsys_c.c b/src/subsys_c.c
index a54ad86..13a919f 100644
--- a/src/subsys_c.c
+++ b/src/subsys_c.c
@@ -18,6 +18,6 @@ int nmi_subsys_dbgerror(const char *arg, char **err_out) {
 
 int nmi_subsys_kfmon(const char *arg, char **err_out) {
     #define NMI_ERR_RET 1
-    NMI_RETURN_ERR("not implemented yet"); // TODO
+    NMI_RETURN_ERR("not implemented yet (arg=%s)", arg); // TODO
     #undef NMI_ERR_RET
 }