diff --git a/src/sharpapi/exceptions.py b/src/sharpapi/exceptions.py
index 14c5d17..42c8fef 100644
--- a/src/sharpapi/exceptions.py
+++ b/src/sharpapi/exceptions.py
@@ -82,6 +82,7 @@ class StreamError(SharpAPIError):
 METHOD_NOT_ALLOWED = "method_not_allowed"
 MISSING_API_KEY = "missing_api_key"
 NOT_FOUND = "not_found"
+NOT_READY = "not_ready"
 RATE_LIMITED = "rate_limited"
 SERVICE_UNAVAILABLE = "service_unavailable"
 TIER_RESTRICTED = "tier_restricted"
@@ -113,6 +114,7 @@ class StreamError(SharpAPIError):
     METHOD_NOT_ALLOWED: "HTTP method not allowed on this endpoint.",
     MISSING_API_KEY: "No API key provided.",
     NOT_FOUND: "Resource not found.",
+    NOT_READY: "A required backing store is not yet ready to serve this request; retry shortly.",
     RATE_LIMITED: "Rate limit exceeded; see Retry-After header.",
     SERVICE_UNAVAILABLE: "Service is temporarily unavailable.",
     TIER_RESTRICTED: "Current subscription tier does not include this feature.",
@@ -160,6 +162,7 @@ class StreamError(SharpAPIError):
     INTERNAL_ERROR: SharpAPIError,
     METHOD_NOT_ALLOWED: SharpAPIError,
     NOT_FOUND: SharpAPIError,
+    NOT_READY: SharpAPIError,
     SERVICE_UNAVAILABLE: SharpAPIError,
     UNKNOWN_ENDPOINT: SharpAPIError,
     UPSTREAM_ERROR: SharpAPIError,