diff --git a/monero/numbers.py b/monero/numbers.py
index c2c9973..a5ddd18 100644
--- a/monero/numbers.py
+++ b/monero/numbers.py
@@ -13,6 +13,9 @@ else:                       # pragma: no cover
 
 def to_atomic(amount):
     """Convert Monero decimal to atomic integer of piconero."""
+    if not isinstance(amount, (Decimal, float) + _integer_types):
+        raise ValueError("Amount '{}' doesn't have numeric type. Only Decimal, int, long and "
+                "float (not recommended) are accepted as amounts.")
     return int(amount * 10**12)
 
 def from_atomic(amount):
diff --git a/tests/test_numbers.py b/tests/test_numbers.py
index df96952..0640a5f 100644
--- a/tests/test_numbers.py
+++ b/tests/test_numbers.py
@@ -1,4 +1,5 @@
 from decimal import Decimal
+import sys
 import unittest
 
 from monero.numbers import to_atomic, from_atomic, as_monero, PaymentID
@@ -12,6 +13,14 @@ class NumbersTestCase(unittest.TestCase):
         self.assertEqual(to_atomic(Decimal('0.000000000001')), 1)
         self.assertEqual(from_atomic(1), Decimal('0.000000000001'))
 
+    def test_numeric_types(self):
+        "Only check if conversion of given type succeeds or fails."
+        self.assertTrue(to_atomic(1))
+        self.assertTrue(to_atomic(1.0))
+        if hasattr(sys, 'maxint'):  # Python 2.x
+            self.assertTrue(to_atomic(sys.maxint + 1))
+        self.assertRaises(ValueError, to_atomic, '1')
+
     def test_rounding(self):
         self.assertEqual(to_atomic(Decimal('1.0000000000004')), 1000000000000)
         self.assertEqual(as_monero(Decimal('1.0000000000014')), Decimal('1.000000000001'))