diff -uNr fluxbox-1.3.7/src/FbCommands.cc fluxbox-1.3.7.mod/src/FbCommands.cc
--- fluxbox-1.3.7/src/FbCommands.cc	2015-02-08 12:44:45.353187009 +0200
+++ fluxbox-1.3.7.mod/src/FbCommands.cc	2018-06-19 20:52:20.788391222 +0300
@@ -153,7 +153,7 @@
     // this process exits immediately, so we don't have to worry about memleaks
     const char *shell = getenv("SHELL");
     if (!shell)
-        shell = "/bin/sh";
+        shell = "@TERMUX_PREFIX@/bin/sh";
 
     setsid();
     execl(shell, shell, "-c", m_cmd.c_str(), static_cast<void*>(NULL));