diff --git a/Makefile b/Makefile
index ab29b1b..6bf6a57 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,8 @@ INCLUDE=include
 
 COMMON_FLAGS= -W -Wall -pedantic -fno-strict-aliasing $(addprefix -I,$(INCLUDE))
 
-OPT_FLAGS?= -march=native -fgraphite -fopenmp -floop-parallelize-all -ftree-parallelize-loops=4 \
+MARCH?= -march=native
+OPT_FLAGS?= $(MARCH) -fgraphite -fopenmp -floop-parallelize-all -ftree-parallelize-loops=4 \
 	    -floop-interchange -ftree-loop-distribution -floop-strip-mine -floop-block \
 	    -fno-stack-check
 
diff --git a/src/bits.c b/src/bits.c
index 2fc0ac8..0a8e6f0 100644
--- a/src/bits.c
+++ b/src/bits.c
@@ -15,7 +15,8 @@
 
 static inline int sfread(void* out, size_t *restrict size, FILE* f)
 {
-	return !!(*size = (size_t)fread(out, 1, *size, f));
+	register ssize_t r = fread(out, 1, *size, f);
+	return r < 0 ? (perror("failed to read from stdin"), 0) : !!(*size = (size_t)r);
 }
 
 static int fwrite_all(const void* _buf, size_t sz, size_t num, FILE* out)