diff --git a/Makefile b/Makefile
index 58a93bb55..38e8fd71e 100644
--- a/Makefile
+++ b/Makefile
@@ -31,14 +31,7 @@ LDFLAGS = -Map ../../$(MAP)
 
 LIB := -L ../../tools/agbcc/lib -lgcc -lc
 
-ifeq ($(OS),Windows_NT)
-	SHA1 := sha1sum -c
-else ifeq ($(shell uname -s),Darwin)
-	SHA1 := shasum -c
-else
-	SHA1 := sha1sum -c
-endif
-
+SHA1SUM := $(shell { command -v sha1sum || command -v shasum; } 2>/dev/null) -c
 GFX := tools/gbagfx/gbagfx
 AIF := tools/aif2pcm/aif2pcm
 MID := $(abspath tools/mid2agb/mid2agb)