diff --git a/Makefile b/Makefile
index 5386821..eb5db3e 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
-CC = gcc
-CFLAGS = -g -O2 -MMD
+CC ?= gcc
+CFLAGS += -MMD
 
 OBJS = \
 	hcalc.o \
@@ -10,7 +10,7 @@ OBJS = \
 	$E
 
 hcalc : $(OBJS)
-	gcc -o $@ $^ -L/usr/X11R6/lib -lXpm -lX11
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $^ -lXpm -lX11
 
 clean :
 	-rm -f *.o *.d *~ \#* hcalc core
diff --git a/draw.c b/draw.c
index 5bde83d..c3bdeb2 100644
--- a/draw.c
+++ b/draw.c
@@ -3,6 +3,7 @@
    http://www.delorie.com/store/hcalc/
 */
 #include "hcalc.h"
+#include <string.h>
 
 static char shown_offsets[15];
 static int shown_bitmask;
diff --git a/input.c b/input.c
index d7de47c..f1d45f5 100644
--- a/input.c
+++ b/input.c
@@ -5,6 +5,7 @@
 #include "hcalc.h"
 #include <ctype.h>
 #include <string.h>
+#include <stdlib.h>
 
 char pending_op = 0;
 int making_number = 0;
diff --git a/setupx.c b/setupx.c
index 238c1e2..74e574b 100644
--- a/setupx.c
+++ b/setupx.c
@@ -3,6 +3,7 @@
    http://www.delorie.com/store/hcalc/
 */
 #include "hcalc.h"
+#include <stdlib.h>
 
 Display *display=0;
 int screen=0;