diff --git a/src/agent.c b/src/agent.c
index 3a15183e..0fe1c5f7 100644
--- a/src/agent.c
+++ b/src/agent.c
@@ -1129,6 +1129,10 @@ LIBSSH2_AGENT *libssh2_agent_init(LIBSSH2_SESSION *session)
 int libssh2_agent_connect(LIBSSH2_AGENT *agent)
 {
     int i, rc = LIBSSH2_ERROR_METHOD_NOT_SUPPORTED;
+
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     for(i = 0; agent_supported_backends[i].name; i++) {
         agent->ops = agent_supported_backends[i].ops;
         rc = agent->ops->connect(agent);
@@ -1145,6 +1149,9 @@ int libssh2_agent_connect(LIBSSH2_AGENT *agent)
  */
 int libssh2_agent_list_identities(LIBSSH2_AGENT *agent)
 {
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     memset(&agent->transctx, 0, sizeof(agent->transctx));
     /* Abandon the last fetched identities */
     agent_free_identities(agent);
@@ -1166,6 +1173,10 @@ int libssh2_agent_get_identity(LIBSSH2_AGENT *agent,
                                struct libssh2_agent_publickey *prev)
 {
     struct agent_publickey *node;
+
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     if(prev && prev->node) {
         /* we have a starting point */
         struct agent_publickey *prev_node = prev->node;
@@ -1197,6 +1208,9 @@ int libssh2_agent_userauth(LIBSSH2_AGENT *agent,
     void *abstract = agent;
     int rc;
 
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     if(agent->session->userauth_pblc_state == ssh2_NB_state_idle) {
         memset(&agent->transctx, 0, sizeof(agent->transctx));
         agent->identity = identity->node;
@@ -1230,6 +1244,9 @@ int libssh2_agent_sign(LIBSSH2_AGENT *agent,
     int rc;
     uint32_t key_kind_len;
 
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     if(agent->session->userauth_pblc_state == ssh2_NB_state_idle) {
         memset(&agent->transctx, 0, sizeof(agent->transctx));
         agent->identity = identity->node;
@@ -1273,6 +1290,9 @@ cleanup:
  */
 int libssh2_agent_disconnect(LIBSSH2_AGENT *agent)
 {
+    if(!agent)
+        return LIBSSH2_ERROR_BAD_USE;
+
     if(agent->ops && agent->fd != LIBSSH2_INVALID_SOCKET)
         return agent->ops->disconnect(agent);
     return LIBSSH2_ERROR_NONE;
@@ -1284,6 +1304,9 @@ int libssh2_agent_disconnect(LIBSSH2_AGENT *agent)
  */
 void libssh2_agent_free(LIBSSH2_AGENT *agent)
 {
+    if(!agent)
+        return;
+
     /* Allow connection freeing when the socket has lost its connection */
     if(agent->fd != LIBSSH2_INVALID_SOCKET)
         libssh2_agent_disconnect(agent);
@@ -1300,6 +1323,9 @@ void libssh2_agent_free(LIBSSH2_AGENT *agent)
  */
 void libssh2_agent_set_identity_path(LIBSSH2_AGENT *agent, const char *path)
 {
+    if(!agent)
+        return;
+
     if(agent->identity_agent_path)
         SSH2_SAFEFREE(agent->session, agent->identity_agent_path);
 
@@ -1321,5 +1347,8 @@ void libssh2_agent_set_identity_path(LIBSSH2_AGENT *agent, const char *path)
  */
 const char *libssh2_agent_get_identity_path(LIBSSH2_AGENT *agent)
 {
+    if(!agent)
+        return NULL;
+
     return agent->identity_agent_path;
 }