diff --git a/librank/librank.c b/librank/librank.c
index 2e3c3fc..28322b9 100644
--- a/librank/librank.c
+++ b/librank/librank.c
@@ -443,13 +443,20 @@
 }
 
 static int getprocname(pid_t pid, char *buf, size_t len) {
-    char filename[20];
+    char filename[32];
     FILE *f;
 
-    sprintf(filename, "/proc/%d/cmdline", pid);
+    snprintf(filename, sizeof(filename), "/proc/%d/cmdline", pid);
     f = fopen(filename, "r");
-    if (!f) { *buf = '\0'; return 1; }
-    if (!fgets(buf, len, f)) { *buf = '\0'; return 2; }
+    if (!f) {
+        *buf = '\0';
+        return 1;
+    }
+    if (!fgets(buf, len, f)) {
+        *buf = '\0';
+        fclose(f);
+        return 2;
+    }
     fclose(f);
     return 0;
 }