diff --git a/src/auth.c b/src/auth.c
index 295f3451..94aaf05f 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -2501,6 +2501,11 @@ int ssh_userauth_gssapi_keyex(ssh_session session)
         return SSH_ERROR;
     }
 
+    if (session->gssapi == NULL) {
+        ssh_set_error(session, SSH_FATAL, "GSSAPI context not initialized");
+        return SSH_ERROR;
+    }
+
     rc = ssh_userauth_request_service(session);
     if (rc == SSH_AGAIN) {
         return SSH_AUTH_AGAIN;
diff --git a/src/gssapi.c b/src/gssapi.c
index 21565528..94ecee22 100644
--- a/src/gssapi.c
+++ b/src/gssapi.c
@@ -1205,6 +1205,11 @@ int ssh_gssapi_auth_keyex_mic(ssh_session session,
     gss_buffer_desc mic_buf = GSS_C_EMPTY_BUFFER;
     OM_uint32 maj_stat, min_stat;
 
+    if (session->gssapi == NULL || session->gssapi->ctx == NULL) {
+        ssh_set_error(session, SSH_FATAL, "GSSAPI context not initialized");
+        return SSH_ERROR;
+    }
+
     buf = ssh_gssapi_build_mic(session, "gssapi-keyex");
     if (buf == NULL) {
         ssh_set_error_oom(session);
diff --git a/src/messages.c b/src/messages.c
index ce0bc7a5..5372c612 100644
--- a/src/messages.c
+++ b/src/messages.c
@@ -1163,6 +1163,12 @@ SSH_PACKET_CALLBACK(ssh_packet_userauth_request)
             goto error;
         }
 
+        if (session->gssapi == NULL || session->gssapi->ctx == NULL) {
+            ssh_set_error(session, SSH_FATAL, "GSSAPI context not initialized");
+            ssh_auth_reply_default(session, 0);
+            goto error;
+        }
+
         rc = ssh_buffer_unpack(packet, "S", &mic_token_string);
         if (rc != SSH_OK) {
             ssh_auth_reply_default(session, 0);
diff --git a/src/packet_cb.c b/src/packet_cb.c
index 0da24f2e..0fee5d48 100644
--- a/src/packet_cb.c
+++ b/src/packet_cb.c
@@ -182,6 +182,11 @@ SSH_PACKET_CALLBACK(ssh_packet_newkeys)
             OM_uint32 maj_stat, min_stat;
             gss_buffer_desc mic = GSS_C_EMPTY_BUFFER, msg = GSS_C_EMPTY_BUFFER;
 
+            if (session->gssapi == NULL || session->gssapi->ctx == NULL) {
+                ssh_set_error(session, SSH_FATAL, "GSSAPI context not initialized");
+                goto error;
+            }
+
             mic.length = ssh_string_len(session->gssapi_key_exchange_mic);
             mic.value = ssh_string_data(session->gssapi_key_exchange_mic);