diff --git a/include/libssh2.h b/include/libssh2.h
index 96c7073..ccc8afd 100644
--- a/include/libssh2.h
+++ b/include/libssh2.h
@@ -380,7 +380,7 @@ LIBSSH2_API int libssh2_channel_forward_cancel(LIBSSH2_LISTENER *listener);
 
 LIBSSH2_API LIBSSH2_CHANNEL *libssh2_channel_forward_accept(LIBSSH2_LISTENER *listener);
 
-LIBSSH2_API int libssh2_channel_setenv_ex(LIBSSH2_CHANNEL *channel, char *varname, unsigned int varname_len, const char *value, unsigned int value_len);
+LIBSSH2_API int libssh2_channel_setenv_ex(LIBSSH2_CHANNEL *channel, const char *varname, unsigned int varname_len, const char *value, unsigned int value_len);
 #define libssh2_channel_setenv(channel, varname, value) libssh2_channel_setenv_ex((channel), (varname), strlen(varname), (value), strlen(value))
 
 LIBSSH2_API int libssh2_channel_request_pty_ex(LIBSSH2_CHANNEL *channel, const char *term, unsigned int term_len, const char *modes, unsigned int modes_len, int width, int height, int width_px, int height_px);
diff --git a/src/channel.c b/src/channel.c
index f996fac..18a1fe2 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -700,7 +700,7 @@ libssh2_channel_forward_accept(LIBSSH2_LISTENER * listener)
  * Set an environment variable prior to requesting a shell/program/subsystem
  */
 LIBSSH2_API int
-libssh2_channel_setenv_ex(LIBSSH2_CHANNEL * channel, char *varname,
+libssh2_channel_setenv_ex(LIBSSH2_CHANNEL * channel, const char *varname,
                           unsigned int varname_len, const char *value,
                           unsigned int value_len)
 {