diff --git a/google/cloud/storage/blob.py b/google/cloud/storage/blob.py
index 4129675c8..ce24d719f 100644
--- a/google/cloud/storage/blob.py
+++ b/google/cloud/storage/blob.py
@@ -55,7 +55,7 @@
 from google.cloud import exceptions
 from google.cloud._helpers import _bytes_to_unicode
 from google.cloud._helpers import _datetime_to_rfc3339
-from google.cloud._helpers import _rfc3339_to_datetime
+from google.cloud._helpers import _rfc3339_nanos_to_datetime
 from google.cloud._helpers import _to_bytes
 from google.cloud.exceptions import NotFound
 from google.cloud.storage._helpers import _add_generation_match_parameters
@@ -3645,7 +3645,7 @@ def retention_expiration_time(self):
         """
         value = self._properties.get("retentionExpirationTime")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def self_link(self):
@@ -3731,7 +3731,7 @@ def time_deleted(self):
         """
         value = self._properties.get("timeDeleted")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def time_created(self):
@@ -3746,7 +3746,7 @@ def time_created(self):
         """
         value = self._properties.get("timeCreated")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def updated(self):
@@ -3761,7 +3761,7 @@ def updated(self):
         """
         value = self._properties.get("updated")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def custom_time(self):
@@ -3776,7 +3776,7 @@ def custom_time(self):
         """
         value = self._properties.get("customTime")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @custom_time.setter
     def custom_time(self, value):
diff --git a/google/cloud/storage/bucket.py b/google/cloud/storage/bucket.py
index 31a188134..76715d835 100644
--- a/google/cloud/storage/bucket.py
+++ b/google/cloud/storage/bucket.py
@@ -28,7 +28,7 @@
 from google.api_core import datetime_helpers
 from google.cloud._helpers import _datetime_to_rfc3339
 from google.cloud._helpers import _NOW
-from google.cloud._helpers import _rfc3339_to_datetime
+from google.cloud._helpers import _rfc3339_nanos_to_datetime
 from google.cloud.exceptions import NotFound
 from google.api_core.iam import Policy
 from google.cloud.storage import _signing
@@ -499,7 +499,7 @@ def uniform_bucket_level_access_locked_time(self):
         ubla = self.get("uniformBucketLevelAccess", {})
         stamp = ubla.get("lockedTime")
         if stamp is not None:
-            stamp = _rfc3339_to_datetime(stamp)
+            stamp = _rfc3339_nanos_to_datetime(stamp)
         return stamp
 
     @property
@@ -2556,7 +2556,7 @@ def retention_policy_effective_time(self):
         if policy is not None:
             timestamp = policy.get("effectiveTime")
             if timestamp is not None:
-                return _rfc3339_to_datetime(timestamp)
+                return _rfc3339_nanos_to_datetime(timestamp)
 
     @property
     def retention_policy_locked(self):
@@ -2675,7 +2675,7 @@ def time_created(self):
         """
         value = self._properties.get("timeCreated")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def versioning_enabled(self):
diff --git a/google/cloud/storage/hmac_key.py b/google/cloud/storage/hmac_key.py
index 47ca33cfc..3fd49079e 100644
--- a/google/cloud/storage/hmac_key.py
+++ b/google/cloud/storage/hmac_key.py
@@ -13,7 +13,7 @@
 # limitations under the License.
 
 from google.cloud.exceptions import NotFound
-from google.cloud._helpers import _rfc3339_to_datetime
+from google.cloud._helpers import _rfc3339_nanos_to_datetime
 
 from google.cloud.storage.constants import _DEFAULT_TIMEOUT
 from google.cloud.storage.retry import DEFAULT_RETRY
@@ -151,7 +151,7 @@ def time_created(self):
         """
         value = self._properties.get("timeCreated")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def updated(self):
@@ -164,7 +164,7 @@ def updated(self):
         """
         value = self._properties.get("updated")
         if value is not None:
-            return _rfc3339_to_datetime(value)
+            return _rfc3339_nanos_to_datetime(value)
 
     @property
     def path(self):
diff --git a/tests/system/test_system.py b/tests/system/test_system.py
index bb6ff5b54..5973e6c73 100644
--- a/tests/system/test_system.py
+++ b/tests/system/test_system.py
@@ -1063,6 +1063,21 @@ def test_upload_blob_custom_time(self):
         custom_time = same_blob.custom_time.replace(tzinfo=None)
         self.assertEqual(custom_time, current_time)
 
+    def test_blob_custom_time_no_micros(self):
+        # Test that timestamps without microseconds are treated correctly by
+        # custom_time encoding/decoding.
+        blob = self.bucket.blob("CustomTimeNoMicrosBlob")
+        file_contents = b"Hello World"
+        time_without_micros = datetime.datetime(2021, 2, 10, 12, 30)
+        blob.custom_time = time_without_micros
+        blob.upload_from_string(file_contents)
+        self.case_blobs_to_delete.append(blob)
+
+        same_blob = self.bucket.blob(("CustomTimeNoMicrosBlob"))
+        same_blob.reload(projection="full")
+        custom_time = same_blob.custom_time.replace(tzinfo=None)
+        self.assertEqual(custom_time, time_without_micros)
+
     def test_blob_crc32_md5_hash(self):
         blob = self.bucket.blob("MyBuffer")
         file_contents = b"Hello World"