diff --git a/src/mainwin.c b/src/mainwin.c
index e153a4c..3745c08 100644
--- a/src/mainwin.c
+++ b/src/mainwin.c
@@ -599,16 +599,18 @@ void set_start_stop_button_hotkey_text()
 	if (config->button1 != -1)
 	{
 		const char *button_1_key = keycode_to_string(display, config->button1);
-		start_text = malloc(strlen(start_text_1) + strlen(button_1_key) + strlen(button_2_key) + 4);
-		stop_text = malloc(strlen(stop_text_1) + strlen(button_1_key) + strlen(button_2_key) + 4);
+		// Allocate space for formatted string with null terminator
+		start_text = malloc(strlen(start_text_1) + strlen(button_1_key) + strlen(button_2_key) + 4 + 1);
+		stop_text = malloc(strlen(stop_text_1) + strlen(button_1_key) + strlen(button_2_key) + 4 + 1);
 		sprintf(start_text, "%s (%s+%s)", start_text_1, button_1_key, button_2_key);
 		sprintf(stop_text, "%s (%s+%s)", stop_text_1, button_1_key, button_2_key);
 	}
 	// Only one key
 	else
 	{
-		start_text = malloc(strlen(start_text_1) + strlen(button_2_key) + 3);
-		stop_text = malloc(strlen(stop_text_1) + strlen(button_2_key) + 3);
+		// Allocate space for formatted string with null terminator
+		start_text = malloc(strlen(start_text_1) + strlen(button_2_key) + 3 + 1);
+		stop_text = malloc(strlen(stop_text_1) + strlen(button_2_key) + 3 + 1);
 		sprintf(start_text, "%s (%s)", start_text_1, button_2_key);
 		sprintf(stop_text, "%s (%s)", stop_text_1, button_2_key);
 	}