diff --git a/drl2gp/drl2gp.c b/drl2gp/drl2gp.c
index 4f43fc3..bd03269 100644
--- a/drl2gp/drl2gp.c
+++ b/drl2gp/drl2gp.c
@@ -22,6 +22,7 @@
  */
 
 
+#include <stdarg.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <ctype.h>
@@ -47,6 +48,19 @@ static double depth, d0, d1;
 #define	MIL2MM(mil)	IN2MM((mil)/1000)
 
 
+static void eprintf(const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	if (vprintf(fmt, ap) < 0) {
+		perror("stdout");
+		exit(1);
+	}
+	va_end(ap);
+}
+
+
 static void header(void)
 {
 	enum {
@@ -182,12 +196,12 @@ static void half_circle(double cx, double cy, double rx, double ry, double s)
 	m[3] = m[0];
 
 	for (a = 0; a < M_PI; a += s) {
-		printf("%f %f %f\n", cx+x, cy+y, -depth);
+		eprintf("%f %f %f\n", cx+x, cy+y, -depth);
 		tmp = x*m[0]+y*m[1];
 		y = x*m[2]+y*m[3];
 		x = tmp;
 	}
-	printf("%f %f %f\n", cx-rx, cy-ry, -depth);
+	eprintf("%f %f %f\n", cx-rx, cy-ry, -depth);
 }
 
 
@@ -208,7 +222,7 @@ static void slot(double xa, double ya, double xb, double yb, double d)
 
 	half_circle(xa, ya, nx, ny, s);
 	half_circle(xb, yb, -nx, -ny, s);
-	printf("%f %f %f\n\n", xa+nx, ya+ny, -depth);
+	eprintf("%f %f %f\n\n", xa+nx, ya+ny, -depth);
 }
 
 
@@ -221,15 +235,15 @@ static void circle(double cx, double cy, double d)
 
 	assert(mill);
 	for (a = 0; a < 2*M_PI; a += s)
-		printf("%f %f %f\n",
+		eprintf("%f %f %f\n",
 		    cx+(cr-tr)*cos(a), cy+(cr-tr)*sin(a), -depth);
-	printf("%f %f %f\n\n", cx+(cr-tr), cy, -depth);
+	eprintf("%f %f %f\n\n", cx+(cr-tr), cy, -depth);
 }
 
 
 static void drill(double x, double y)
 {
-	printf("%f %f %f\n\n", x, y, -depth);
+	eprintf("%f %f %f\n\n", x, y, -depth);
 }
 
 
@@ -443,5 +457,10 @@ int main(int argc, char **argv)
 	header();
 	body();
 
+	if (fflush(stdout) == EOF) {
+		perror("stdout");
+		exit(1);
+	}
+
 	return 0;
 }