diff --git a/agent/ssh/ssh.go b/agent/ssh/ssh.go
index b319552..dba36f0 100644
--- a/agent/ssh/ssh.go
+++ b/agent/ssh/ssh.go
@@ -110,6 +110,10 @@ func (vaultAgent vaultAgent) SignWithFlags(key ssh.PublicKey, data []byte, flags
 		}
 	}
 
+	if sshKey == nil {
+		return nil, errors.New("key not found")
+	}
+
 	isGit := false
 	magicHeader := []byte("SSHSIG\x00\x00\x00\x03git")
 	if bytes.HasPrefix(data, magicHeader) {