diff --git a/runtime/.gitignore b/runtime/.gitignore
index 26525d973..c7d8fe368 100644
--- a/runtime/.gitignore
+++ b/runtime/.gitignore
@@ -1,5 +1,6 @@
-## Ignore all *.a and *.o files
+## Ignore all *.a, *.d, and *.o files
 *.a
+*.d
 *.o
 
 /gdtoa/
diff --git a/runtime/Makefile b/runtime/Makefile
index 5c4c91186..ae0402480 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -297,7 +297,14 @@ libmlton-pic.a: $(MLTON_PIC_OBJS)
 gen/sizes: gen/gen-sizes$(EXE)
 	./gen/gen-sizes > gen/sizes
 
-gen/gen-sizes$(EXE): gen/gen-sizes.c util.o $(HFILES)
+gen/gen-sizes$(EXE).d: gen/gen-sizes.c
+	$(CROSS_PREFIX)$(CC) $(OPTCFLAGS) -M -MG -MT gen/gen-sizes$(EXE) -MT gen/gen-sizes$(EXE).d -MF gen/gen-sizes$(EXE).d gen/gen-sizes.c
+
+ifneq ($(MAKECMDGOALS),clean)
+-include gen/gen-sizes$(EXE).d
+endif
+
+gen/gen-sizes$(EXE): util.o
 	$(CROSS_PREFIX)$(CC) $(OPTCFLAGS) -o gen/gen-sizes gen/gen-sizes.c util.o