diff --git a/src/tablib/core.py b/src/tablib/core.py
index 06624b42..ef3f6fe2 100644
--- a/src/tablib/core.py
+++ b/src/tablib/core.py
@@ -457,12 +457,13 @@ def insert(self, index, row, tags=()):
 
         The default behaviour is to insert the given row to the :class:`Dataset`
         object at the given index.
-       """
+        """
 
         self._validate(row)
-        for pos, func in self._dynamic_columns.items():
-            row = list(row)
-            row.insert(pos, func(row))
+        if len(row) < self.width:
+            for pos, func in self._dynamic_columns.items():
+                row = list(row)
+                row.insert(pos, func(row))
         self._data.insert(index, Row(row, tags=tags))
 
     def rpush(self, row, tags=()):
@@ -560,7 +561,7 @@ def insert_col(self, index, col=None, header=None):
             col = []
 
         # Callable Columns...
-        if hasattr(col, '__call__'):
+        if callable(col):
             self._dynamic_columns[self.width] = col
             col = list(map(col, self._data))
 
diff --git a/tests/test_tablib.py b/tests/test_tablib.py
index a77823a8..a335c44b 100755
--- a/tests/test_tablib.py
+++ b/tests/test_tablib.py
@@ -196,6 +196,8 @@ def initials(row):
         # Also acceptable when all dynamic column values are provided.
         self.founders.append(('Other', 'Second', 84, 'Other', 'OS'))
 
+        self.assertEqual(self.founders[3], ('Some', 'One', 71, 'Some', 'SO'))
+        self.assertEqual(self.founders[4], ('Other', 'Second', 84, 'Other', 'OS'))
         self.assertEqual(
             self.founders['first_again'],
             ['John', 'George', 'Thomas', 'Some', 'Other']