diff --git a/quinn-proto/src/config/mod.rs b/quinn-proto/src/config/mod.rs
index 654e663f3..9cb4a45ed 100644
--- a/quinn-proto/src/config/mod.rs
+++ b/quinn-proto/src/config/mod.rs
@@ -17,7 +17,7 @@ use crate::{
     cid_generator::{ConnectionIdGenerator, HashedConnectionIdGenerator},
     crypto::{self, HandshakeTokenKey, HmacKey},
     shared::ConnectionId,
-    Duration, RandomConnectionIdGenerator, VarInt, VarIntBoundsExceeded,
+    Duration, RandomConnectionIdGenerator, SystemTime, VarInt, VarIntBoundsExceeded,
     DEFAULT_SUPPORTED_VERSIONS, MAX_CID_SIZE,
 };
 
@@ -216,6 +216,8 @@ pub struct ServerConfig {
     pub(crate) max_incoming: usize,
     pub(crate) incoming_buffer_size: u64,
     pub(crate) incoming_buffer_size_total: u64,
+
+    pub(crate) time_source: Arc<dyn TimeSource>,
 }
 
 impl ServerConfig {
@@ -239,6 +241,8 @@ impl ServerConfig {
             max_incoming: 1 << 16,
             incoming_buffer_size: 10 << 20,
             incoming_buffer_size_total: 100 << 20,
+
+            time_source: Arc::new(StdSystemTime),
         }
     }
 
@@ -334,6 +338,16 @@ impl ServerConfig {
         self.incoming_buffer_size_total = incoming_buffer_size_total;
         self
     }
+
+    /// Object to get current [`SystemTime`]
+    ///
+    /// This exists to allow system time to be mocked in tests, or wherever else desired.
+    ///
+    /// Defaults to [`StdSystemTime`], which simply calls [`SystemTime::now()`](SystemTime::now).
+    pub fn time_source(&mut self, time_source: Arc<dyn TimeSource>) -> &mut Self {
+        self.time_source = time_source;
+        self
+    }
 }
 
 #[cfg(any(feature = "rustls-aws-lc-rs", feature = "rustls-ring"))]
@@ -388,6 +402,7 @@ impl fmt::Debug for ServerConfig {
                 "incoming_buffer_size_total",
                 &self.incoming_buffer_size_total,
             )
+            // system_time_clock not debug
             .finish_non_exhaustive()
     }
 }
@@ -503,3 +518,22 @@ impl From<VarIntBoundsExceeded> for ConfigError {
         Self::OutOfBounds
     }
 }
+
+/// Object to get current [`SystemTime`]
+///
+/// This exists to allow system time to be mocked in tests, or wherever else desired.
+pub trait TimeSource: Send + Sync {
+    /// Get [`SystemTime::now()`](SystemTime::now) or the mocked equivalent
+    fn now(&self) -> SystemTime;
+}
+
+/// Default implementation of [`TimeSource`]
+///
+/// Implements `now` by calling [`SystemTime::now()`](SystemTime::now).
+pub struct StdSystemTime;
+
+impl TimeSource for StdSystemTime {
+    fn now(&self) -> SystemTime {
+        SystemTime::now()
+    }
+}
diff --git a/quinn-proto/src/endpoint.rs b/quinn-proto/src/endpoint.rs
index 9f9820261..b0a5e269c 100644
--- a/quinn-proto/src/endpoint.rs
+++ b/quinn-proto/src/endpoint.rs
@@ -31,8 +31,8 @@ use crate::{
     },
     token,
     transport_parameters::{PreferredAddress, TransportParameters},
-    Duration, Instant, ResetToken, RetryToken, Side, SystemTime, Transmit, TransportConfig,
-    TransportError, INITIAL_MTU, MAX_CID_SIZE, MIN_INITIAL_SIZE, RESET_TOKEN_SIZE,
+    Duration, Instant, ResetToken, RetryToken, Side, Transmit, TransportConfig, TransportError,
+    INITIAL_MTU, MAX_CID_SIZE, MIN_INITIAL_SIZE, RESET_TOKEN_SIZE,
 };
 
 /// The main entry point to the library
@@ -506,7 +506,8 @@ impl Endpoint {
                 &header.token,
             ) {
                 Ok(token)
-                    if token.issued + server_config.retry_token_lifetime > SystemTime::now() =>
+                    if token.issued + server_config.retry_token_lifetime
+                        > server_config.time_source.now() =>
                 {
                     (Some(header.dst_cid), token.orig_dst_cid)
                 }
@@ -769,7 +770,7 @@ impl Endpoint {
 
         let token = RetryToken {
             orig_dst_cid: incoming.packet.header.dst_cid,
-            issued: SystemTime::now(),
+            issued: server_config.time_source.now(),
         }
         .encode(
             &*server_config.token_key,
diff --git a/quinn-proto/src/lib.rs b/quinn-proto/src/lib.rs
index c12a479f3..67f13cb66 100644
--- a/quinn-proto/src/lib.rs
+++ b/quinn-proto/src/lib.rs
@@ -51,7 +51,7 @@ pub use rustls;
 mod config;
 pub use config::{
     AckFrequencyConfig, ClientConfig, ConfigError, EndpointConfig, IdleTimeout, MtuDiscoveryConfig,
-    ServerConfig, TransportConfig,
+    ServerConfig, StdSystemTime, TimeSource, TransportConfig,
 };
 
 pub mod crypto;
diff --git a/quinn/src/lib.rs b/quinn/src/lib.rs
index 84a3821f6..4f6e6ea73 100644
--- a/quinn/src/lib.rs
+++ b/quinn/src/lib.rs
@@ -65,8 +65,9 @@ pub use proto::{
     congestion, crypto, AckFrequencyConfig, ApplicationClose, Chunk, ClientConfig, ClosedStream,
     ConfigError, ConnectError, ConnectionClose, ConnectionError, ConnectionId,
     ConnectionIdGenerator, ConnectionStats, Dir, EcnCodepoint, EndpointConfig, FrameStats,
-    FrameType, IdleTimeout, MtuDiscoveryConfig, PathStats, ServerConfig, Side, StreamId, Transmit,
-    TransportConfig, TransportErrorCode, UdpStats, VarInt, VarIntBoundsExceeded, Written,
+    FrameType, IdleTimeout, MtuDiscoveryConfig, PathStats, ServerConfig, Side, StdSystemTime,
+    StreamId, TimeSource, Transmit, TransportConfig, TransportErrorCode, UdpStats, VarInt,
+    VarIntBoundsExceeded, Written,
 };
 #[cfg(any(feature = "rustls-aws-lc-rs", feature = "rustls-ring"))]
 pub use rustls;