diff --git a/src/chat.c b/src/chat.c
index 75d5cda..c5f1f68 100644
--- a/src/chat.c
+++ b/src/chat.c
@@ -378,7 +378,7 @@ static void chat_onKey(ToxWindow *self, Tox *m, wint_t key)
 #else
     if (isprint(key)) {
 #endif
-        if (ctx->pos <= MAX_STR_SIZE) {
+        if (ctx->pos < (MAX_STR_SIZE-1)) {
             mvwaddstr(self->window, y, x, wc_to_char(key));
             ctx->line[ctx->pos++] = key;
             ctx->line[ctx->pos] = L'\0';
diff --git a/src/prompt.c b/src/prompt.c
index 7b859da..4a772dd 100644
--- a/src/prompt.c
+++ b/src/prompt.c
@@ -136,7 +136,7 @@ static void prompt_onKey(ToxWindow *self, Tox *m, wint_t key)
 
     /* Add printable characters to line */
     else if (isprint(key)) {
-        if (prompt_buf_pos <= MAX_STR_SIZE) {
+        if (prompt_buf_pos < (MAX_STR_SIZE-1)) {
             mvwaddch(self->window, y, x, key);
             prompt_buf[prompt_buf_pos++] = key;
             prompt_buf[prompt_buf_pos] = '\0';