diff --git a/django/db/models/aggregates.py b/django/db/models/aggregates.py
index 1b0f9d98af..ac0b62d0bf 100644
--- a/django/db/models/aggregates.py
+++ b/django/db/models/aggregates.py
@@ -4,7 +4,9 @@ Classes to represent the definitions of aggregate functions.
 from django.core.exceptions import FieldError
 from django.db.models.expressions import Case, Func, Star, When
 from django.db.models.fields import IntegerField
-from django.db.models.functions.mixins import NumericOutputFieldMixin
+from django.db.models.functions.mixins import (
+    FixDurationInputMixin, NumericOutputFieldMixin,
+)
 
 __all__ = [
     'Aggregate', 'Avg', 'Count', 'Max', 'Min', 'StdDev', 'Sum', 'Variance',
@@ -94,25 +96,10 @@ class Aggregate(Func):
         return options
 
 
-class Avg(NumericOutputFieldMixin, Aggregate):
+class Avg(FixDurationInputMixin, NumericOutputFieldMixin, Aggregate):
     function = 'AVG'
     name = 'Avg'
 
-    def as_mysql(self, compiler, connection, **extra_context):
-        sql, params = super().as_sql(compiler, connection, **extra_context)
-        if self.output_field.get_internal_type() == 'DurationField':
-            sql = 'CAST(%s as SIGNED)' % sql
-        return sql, params
-
-    def as_oracle(self, compiler, connection, **extra_context):
-        if self.output_field.get_internal_type() == 'DurationField':
-            expression = self.get_source_expressions()[0]
-            from django.db.backends.oracle.functions import IntervalToSeconds, SecondsToInterval
-            return compiler.compile(
-                SecondsToInterval(Avg(IntervalToSeconds(expression), filter=self.filter))
-            )
-        return super().as_sql(compiler, connection, **extra_context)
-
 
 class Count(Aggregate):
     function = 'COUNT'
@@ -152,25 +139,10 @@ class StdDev(NumericOutputFieldMixin, Aggregate):
         return {**super()._get_repr_options(), 'sample': self.function == 'STDDEV_SAMP'}
 
 
-class Sum(Aggregate):
+class Sum(FixDurationInputMixin, Aggregate):
     function = 'SUM'
     name = 'Sum'
 
-    def as_mysql(self, compiler, connection, **extra_context):
-        sql, params = super().as_sql(compiler, connection, **extra_context)
-        if self.output_field.get_internal_type() == 'DurationField':
-            sql = 'CAST(%s as SIGNED)' % sql
-        return sql, params
-
-    def as_oracle(self, compiler, connection, **extra_context):
-        if self.output_field.get_internal_type() == 'DurationField':
-            expression = self.get_source_expressions()[0]
-            from django.db.backends.oracle.functions import IntervalToSeconds, SecondsToInterval
-            return compiler.compile(
-                SecondsToInterval(Sum(IntervalToSeconds(expression)))
-            )
-        return super().as_sql(compiler, connection, **extra_context)
-
 
 class Variance(NumericOutputFieldMixin, Aggregate):
     name = 'Variance'
diff --git a/django/db/models/functions/mixins.py b/django/db/models/functions/mixins.py
index 9b46987788..8486ddb005 100644
--- a/django/db/models/functions/mixins.py
+++ b/django/db/models/functions/mixins.py
@@ -20,6 +20,25 @@ class FixDecimalInputMixin:
         return clone.as_sql(compiler, connection, **extra_context)
 
 
+class FixDurationInputMixin:
+
+    def as_mysql(self, compiler, connection, **extra_context):
+        sql, params = super().as_sql(compiler, connection, **extra_context)
+        if self.output_field.get_internal_type() == 'DurationField':
+            sql = 'CAST(%s AS SIGNED)' % sql
+        return sql, params
+
+    def as_oracle(self, compiler, connection, **extra_context):
+        if self.output_field.get_internal_type() == 'DurationField':
+            expression = self.get_source_expressions()[0]
+            options = self._get_repr_options()
+            from django.db.backends.oracle.functions import IntervalToSeconds, SecondsToInterval
+            return compiler.compile(
+                SecondsToInterval(self.__class__(IntervalToSeconds(expression), **options))
+            )
+        return super().as_sql(compiler, connection, **extra_context)
+
+
 class NumericOutputFieldMixin:
 
     def _resolve_output_field(self):