diff --git a/src/pyobo/identifier_utils.py b/src/pyobo/identifier_utils.py
index 7c25ac4b..5cbc97e0 100644
--- a/src/pyobo/identifier_utils.py
+++ b/src/pyobo/identifier_utils.py
@@ -118,12 +118,9 @@ def normalize_curie(
             logger.debug(f"could not split CURIE on colon: {curie}")
         return None, None
 
-    # remove redundant prefix
-    if identifier.casefold().startswith(f"{prefix.casefold()}:"):
-        identifier = identifier[len(prefix) + 1 :]
-
     norm_node_prefix = bioregistry.normalize_prefix(prefix)
     if norm_node_prefix:
+        identifier = bioregistry.standardize_identifier(norm_node_prefix, identifier)
         return ReferenceTuple(norm_node_prefix, identifier)
     elif strict:
         raise MissingPrefixError(curie=curie, ontology_prefix=ontology_prefix, node=node)
diff --git a/src/pyobo/normalizer.py b/src/pyobo/normalizer.py
index a9ea604c..6577c87d 100644
--- a/src/pyobo/normalizer.py
+++ b/src/pyobo/normalizer.py
@@ -82,20 +82,17 @@ def _iterate_synonyms_to_identifiers(
         id_to_synonyms: Mapping[str, Iterable[str]],
         remove_prefix: str | None = None,
     ) -> Iterable[tuple[str, str]]:
-        if remove_prefix is not None:
-            remove_prefix = f'{remove_prefix.lower().rstrip(":")}:'
-
         # Add name
         for identifier, name in id_to_name.items():
-            if remove_prefix and identifier.lower().startswith(remove_prefix):
-                identifier = identifier[len(remove_prefix) :]
+            if remove_prefix:
+                identifier = bioregistry.standardize_identifier(remove_prefix, identifier)
 
             yield name, identifier
 
         # Add synonyms
         for identifier, synonyms in id_to_synonyms.items():
-            if remove_prefix and identifier.lower().startswith(remove_prefix):
-                identifier = identifier[len(remove_prefix) :]
+            if remove_prefix:
+                identifier = bioregistry.standardize_identifier(remove_prefix, identifier)
 
             for synonym in synonyms:
                 # it might overwrite but this is probably always due to alternate ids
diff --git a/src/pyobo/struct/reference.py b/src/pyobo/struct/reference.py
index 75bf9a96..6ab451a8 100644
--- a/src/pyobo/struct/reference.py
+++ b/src/pyobo/struct/reference.py
@@ -96,8 +96,6 @@ def from_curie_or_uri(
         if prefix is None or identifier is None:
             return None
 
-        identifier = bioregistry.standardize_identifier(prefix, identifier)
-
         if name is None and auto:
             from ..api import get_name
 
@@ -108,12 +106,8 @@ def from_curie_or_uri(
     def _escaped_identifier(self):
         return obo_escape(self.identifier)
 
-    def __str__(self):
-        identifier_lower = self.identifier.lower()
-        if identifier_lower.startswith(f"{self.prefix.lower()}:"):
-            rv = identifier_lower
-        else:
-            rv = f"{self.preferred_prefix}:{self._escaped_identifier}"
+    def __str__(self) -> str:
+        rv = f"{self.preferred_prefix}:{self._escaped_identifier}"
         if self.name:
             rv = f"{rv} ! {self.name}"
         return rv