diff --git a/src/duc/cmd-cgi.c b/src/duc/cmd-cgi.c
index 7cd3f649..ae2fbe8d 100644
--- a/src/duc/cmd-cgi.c
+++ b/src/duc/cmd-cgi.c
@@ -257,9 +257,11 @@ static void include_file(const char *fname)
 		printf("<!-- start include -->\n");
 		for(;;) {
 			char buf[4096];
-			size_t n = fread(buf, 1, sizeof(buf), f);
-			if(n == 0) break;
-			fwrite(buf, 1, n, stdout);
+			size_t in = fread(buf, 1, sizeof(buf), f);
+			if(in == 0) break;
+			size_t out = fwrite(buf, 1, in, stdout);
+			if(out == 0) break;
+			if(out < in) break;
 		}
 		printf("<!-- end include -->\n");
 		fclose(f);
diff --git a/src/duc/main.c b/src/duc/main.c
index 9a4906e3..287abfe5 100644
--- a/src/duc/main.c
+++ b/src/duc/main.c
@@ -211,6 +211,7 @@ static void printi(const char *s, int pos, int indent, int max)
 	const char *p1 = s;
 	const char *p2 = s;
 	int i;
+	int out;
 
 	while(*p1) {
 		while(*p2 && !isspace(*p2)) p2++;
@@ -222,7 +223,8 @@ static void printi(const char *s, int pos, int indent, int max)
 			pos = indent;
 		}
 
-		fwrite(p1, l, 1, stdout);
+		out = fwrite(p1, l, 1, stdout);
+		if (out == 0) break;
 		while(*p2 && isspace(*p2)) p2++;
 		pos += l;
 		if(pos < max) {
diff --git a/src/libduc-graph/graph-cairo.c b/src/libduc-graph/graph-cairo.c
index 3e832793..3cce0198 100644
--- a/src/libduc-graph/graph-cairo.c
+++ b/src/libduc-graph/graph-cairo.c
@@ -41,7 +41,10 @@ struct cairo_backend_data {
 static cairo_status_t cairo_writer(void *closure, const unsigned char *data, unsigned int length)
 {
 	FILE *f = closure;
-	fwrite(data, length, 1, f);
+	size_t out = fwrite(data, length, 1, f);
+	if (out == 0 || out < length) {
+	    return CAIRO_STATUS_WRITE_ERROR;
+	}
 	return CAIRO_STATUS_SUCCESS;
 }