diff --git a/st.c b/st.c
index b74c90d..e1eab16 100644
--- a/st.c
+++ b/st.c
@@ -909,6 +909,16 @@ execsh(char *cmd, char **args)
 	unsetenv("COLUMNS");
 	unsetenv("LINES");
 	unsetenv("TERMCAP");
+	/*
+	 * A new st window is never inside a multiplexer, even when st itself
+	 * was launched from one. Programs such as kitten icat use these to
+	 * decide whether to wrap escape codes for tmux, which breaks them.
+	 */
+	unsetenv("TMUX");
+	unsetenv("TMUX_PANE");
+	unsetenv("STY");
+	unsetenv("ZELLIJ");
+	unsetenv("ZELLIJ_SESSION_NAME");
 	setenv("LOGNAME", pw->pw_name, 1);
 	setenv("USER", pw->pw_name, 1);
 	setenv("SHELL", sh, 1);