diff --git a/lib/smtp.c b/lib/smtp.c
index 7cbccba088abf0b925a929885524678a145d09c8..073925d1b6e80f62f70c207de3ee17a3637fd4e5 100644
--- a/lib/smtp.c
+++ b/lib/smtp.c
@@ -1039,7 +1039,7 @@ static CURLcode smtp_setup_connection(struct connectdata * conn)
   return CURLE_OK;
 }
 
-CURLcode Curl_smtp_escape_eob(struct connectdata *conn, int nread)
+CURLcode Curl_smtp_escape_eob(struct connectdata *conn, ssize_t nread)
 {
   /* When sending SMTP payload, we must detect CRLF.CRLF sequences in
    * the data and make sure it is sent as CRLF..CRLF instead, as
diff --git a/lib/smtp.h b/lib/smtp.h
index 3531a9652a16117fe7600f80fc3eb027056c7de1..fac43041abb336110c66b623de31388d140a1bc1 100644
--- a/lib/smtp.h
+++ b/lib/smtp.h
@@ -64,6 +64,6 @@ extern const struct Curl_handler Curl_handler_smtps;
 #define SMTP_EOB_REPL "\x0d\x0a\x2e\x2e"
 #define SMTP_EOB_REPL_LEN 4
 
-CURLcode Curl_smtp_escape_eob(struct connectdata *conn, int nread);
+CURLcode Curl_smtp_escape_eob(struct connectdata *conn, ssize_t nread);
 
 #endif /* __SMTP_H */