diff --git a/src/frame.c b/src/frame.c
index 9eada96..f238afe 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -476,7 +476,9 @@ ssize_t patty_ax25_frame_encode(patty_ax25_frame *frame,
     }
 
     if (frame->info && frame->infolen) {
-        if (1 + offset + frame->infolen > len) {
+        if (len < 1 + offset + frame->infolen) {
+            errno = EOVERFLOW;
+
             goto error_toobig;
         }
 
@@ -623,6 +625,8 @@ ssize_t patty_ax25_frame_encode_reply_to(patty_ax25_frame *frame,
 
     if (PATTY_AX25_FRAME_CONTROL_I(reply->control) || PATTY_AX25_FRAME_CONTROL_UI(reply->control)) {
         if (len < 1 + offset + reply->infolen) {
+            errno = EOVERFLOW;
+
             goto error_toobig;
         }