diff --git a/core/data/tests/test_custom_serialize_deserialize_functions/output.py b/core/data/tests/test_custom_serialize_deserialize_functions/output.py
index 71af1dad..6add1753 100644
--- a/core/data/tests/test_custom_serialize_deserialize_functions/output.py
+++ b/core/data/tests/test_custom_serialize_deserialize_functions/output.py
@@ -25,6 +25,11 @@ def parse_rfc3339(date_str: str) -> datetime:
         "%Y-%m-%dT%H:%M:%SZ",   
         "%Y-%m-%dT%H:%M:%S.%fZ"
     ]
+
+    # %f accepts at most 6 fractional digits, but Rust can emit up to 9 (nanoseconds)
+    head, dot, fraction = date_str.partition(".")
+    if dot and fraction.endswith("Z"):
+        date_str = f"{head}.{fraction[:-1][:6]}Z"
     
     for fmt in date_formats:
         try:
diff --git a/core/data/tests/test_serde_iso8601/output.py b/core/data/tests/test_serde_iso8601/output.py
index 246d940c..3a888a70 100644
--- a/core/data/tests/test_serde_iso8601/output.py
+++ b/core/data/tests/test_serde_iso8601/output.py
@@ -13,6 +13,11 @@ def parse_rfc3339(date_str: str) -> datetime:
         "%Y-%m-%dT%H:%M:%SZ",   
         "%Y-%m-%dT%H:%M:%S.%fZ"
     ]
+
+    # %f accepts at most 6 fractional digits, but Rust can emit up to 9 (nanoseconds)
+    head, dot, fraction = date_str.partition(".")
+    if dot and fraction.endswith("Z"):
+        date_str = f"{head}.{fraction[:-1][:6]}Z"
     
     for fmt in date_formats:
         try:
diff --git a/core/src/language/python.rs b/core/src/language/python.rs
index b96d8d6d..0c2f672f 100644
--- a/core/src/language/python.rs
+++ b/core/src/language/python.rs
@@ -798,6 +798,11 @@ fn json_translation_for_type(python_type: &str) -> Option<CustomJsonTranslationF
         "%Y-%m-%dT%H:%M:%SZ",   
         "%Y-%m-%dT%H:%M:%S.%fZ"
     ]
+
+    # %f accepts at most 6 fractional digits, but Rust can emit up to 9 (nanoseconds)
+    head, dot, fraction = date_str.partition(".")
+    if dot and fraction.endswith("Z"):
+        date_str = f"{head}.{fraction[:-1][:6]}Z"
     
     for fmt in date_formats:
         try: