diff --git a/make/ghdl.mk b/make/ghdl.mk
index bad195a..863469b 100644
--- a/make/ghdl.mk
+++ b/make/ghdl.mk
@@ -43,13 +43,13 @@ GHDL_GCC := ghdl-gcc
 
 # Wave format selection
 SIM_FILE-vcd := $(BUILD_DIR)/$(TARGET).vcd
-GTK_OPTS-vcd := --vcd=$(SIM_FILE-VCD)
+GTK_OPTS-vcd := --vcd=$(SIM_FILE-vcd)
 
 SIM_FILE-fst := $(BUILD_DIR)/$(TARGET).fst
-GTK_OPTS-fst := --fst=$(SIM_FILE-FST)
+GTK_OPTS-fst := --fst=$(SIM_FILE-fst)
 
 SIM_FILE-ghw := $(BUILD_DIR)/$(TARGET).ghw
-GTK_OPTS-ghw := --wave=$(SIM_FILE-GHW)
+GTK_OPTS-ghw := --wave=$(SIM_FILE-ghw)
 
 SIM_FILE := $(SIM_FILE-$(WAVE_FORMAT))
 GTK_OPTS := $(GTK_OPTS-$(WAVE_FORMAT))