diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index fccf9f0a26..7c108abcf2 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6636,11 +6636,22 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
             p2 = lock_user(VERIFY_WRITE, arg2, arg3, 0);
             if (!p || !p2) {
                 ret = -TARGET_EFAULT;
+            } else if (!arg3) {
+                /* Short circuit this for the magic exe check. */
+                ret = -TARGET_EINVAL;
             } else if (is_proc_myself((const char *)p, "exe")) {
                 char real[PATH_MAX], *temp;
                 temp = realpath(exec_path, real);
-                ret = temp == NULL ? get_errno(-1) : strlen(real) ;
-                snprintf((char *)p2, arg3, "%s", real);
+                /* Return value is # of bytes that we wrote to the buffer. */
+                if (temp == NULL) {
+                    ret = get_errno(-1);
+                } else {
+                    /* Don't worry about sign mismatch as earlier mapping
+                     * logic would have thrown a bad address error. */
+                    ret = MIN(strlen(real), arg3);
+                    /* We cannot NUL terminate the string. */
+                    memcpy(p2, real, ret);
+                }
             } else {
                 ret = get_errno(readlink(path(p), p2, arg3));
             }