diff --git a/src/internal/oauth/client.zig b/src/internal/oauth/client.zig
index 657cb0a..1b369b7 100644
--- a/src/internal/oauth/client.zig
+++ b/src/internal/oauth/client.zig
@@ -565,7 +565,16 @@ fn fetchWithDpopNonceRetry(
         });
 
         const new_nonce = if (fetch_result.oauth.dpop_nonce) |value| try allocator.dupe(u8, value) else null;
-        if (new_nonce != null and isDpopNonceChallenge(fetch_result.status, fetch_result.body, fetch_result.oauth.www_authenticate)) {
+        const challenged = isDpopNonceChallenge(
+            fetch_result.status,
+            fetch_result.body,
+            fetch_result.oauth.www_authenticate,
+        );
+        const selected_nonce = retainDpopNonce(challenged, new_nonce, nonce) catch |err| {
+            fetch_result.deinit(allocator);
+            return err;
+        };
+        if (challenged) {
             fetch_result.deinit(allocator);
             if (retry_nonce) |value| allocator.free(value);
             retry_nonce = new_nonce.?;
@@ -573,16 +582,11 @@ fn fetchWithDpopNonceRetry(
             continue;
         }
 
-        if (new_nonce == null and retry_nonce == null) {
-            fetch_result.deinit(allocator);
-            return error.MissingDpopNonce;
-        }
-
         const body = fetch_result.body;
         fetch_result.body = &.{};
         const returned_nonce = if (new_nonce) |value|
             value
-        else if (retry_nonce) |value|
+        else if (selected_nonce) |value|
             try allocator.dupe(u8, value)
         else
             null;
@@ -596,6 +600,15 @@ fn fetchWithDpopNonceRetry(
     return error.DpopNonceRetryExhausted;
 }
 
+fn retainDpopNonce(
+    challenged: bool,
+    response_nonce: ?[]const u8,
+    used_nonce: ?[]const u8,
+) !?[]const u8 {
+    if (challenged) return response_nonce orelse error.MissingDpopNonce;
+    return response_nonce orelse used_nonce;
+}
+
 pub fn validateAuthorizationServerMetadata(metadata: AuthorizationServerMetadata) !void {
     try validateSimpleHttpsOrigin(metadata.issuer);
     if (!containsString(metadata.response_types_supported, "code")) return error.InvalidAuthorizationServerMetadata;
@@ -873,6 +886,26 @@ test "DPoP nonce challenge detection" {
     try std.testing.expect(!isDpopNonceChallenge(.ok, "{\"error\":\"use_dpop_nonce\"}", null));
 }
 
+test "DPoP nonce is optional until challenged and retained until replaced" {
+    try std.testing.expect((try retainDpopNonce(false, null, null)) == null);
+    try std.testing.expectEqualStrings(
+        "prior",
+        (try retainDpopNonce(false, null, "prior")).?,
+    );
+    try std.testing.expectEqualStrings(
+        "new",
+        (try retainDpopNonce(false, "new", "prior")).?,
+    );
+    try std.testing.expectError(
+        error.MissingDpopNonce,
+        retainDpopNonce(true, null, null),
+    );
+    try std.testing.expectEqualStrings(
+        "challenge",
+        (try retainDpopNonce(true, "challenge", null)).?,
+    );
+}
+
 test "DPoP htu omits query and fragment" {
     const allocator = std.testing.allocator;
     const htu = try dpopHtu(allocator, "https://pds.example.com/xrpc/com.atproto.repo.getRecord?repo=did%3Aplc%3Aabc#frag");