diff --git a/crates/irtt-client/src/client.rs b/crates/irtt-client/src/client.rs
index 7e69ffc..e5d2e5c 100644
--- a/crates/irtt-client/src/client.rs
+++ b/crates/irtt-client/src/client.rs
@@ -40,6 +40,16 @@ pub struct Client {
 impl Client {
     pub fn connect(config: ClientConfig) -> Result<Self, ClientError> {
         validate_open_timeouts(&config.open_timeouts)?;
+        if config.max_pending_probes == 0 {
+            return Err(ClientError::InvalidConfig {
+                reason: "max_pending_probes must be greater than zero".to_owned(),
+            });
+        }
+        if config.probe_timeout == Duration::ZERO {
+            return Err(ClientError::InvalidConfig {
+                reason: "probe_timeout must be greater than zero".to_owned(),
+            });
+        }
         let remote = resolve_remote(&config)?;
         let socket = connect_udp_socket(&config.socket_config, remote)?;
         let requested = params_from_config(&config)?;
diff --git a/crates/irtt-client/src/error.rs b/crates/irtt-client/src/error.rs
index d5faf76..a9da4a8 100644
--- a/crates/irtt-client/src/error.rs
+++ b/crates/irtt-client/src/error.rs
@@ -43,4 +43,6 @@ pub enum ClientError {
     DurationOverflow,
     #[error("pending probe limit exceeded ({limit})")]
     PendingLimitExceeded { limit: usize },
+    #[error("invalid configuration: {reason}")]
+    InvalidConfig { reason: String },
 }