diff --git a/contracts/SafeMath.sol b/contracts/SafeMath.sol
index e25589724..fd084967d 100644
--- a/contracts/SafeMath.sol
+++ b/contracts/SafeMath.sol
@@ -11,6 +11,13 @@ contract SafeMath {
     return c;
   }
 
+  function safeDiv(uint a, uint b) internal returns (uint) {
+    assert(b > 0);
+    uint c = a / b;
+    assert(a == b * c + a % b);
+    return c;
+  }
+
   function safeSub(uint a, uint b) internal returns (uint) {
     assert(b <= a);
     return a - b;
@@ -22,6 +29,22 @@ contract SafeMath {
     return c;
   }
 
+  function max64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a >= b ? a : b;
+  }
+
+  function min64(uint64 a, uint64 b) internal constant returns (uint64) {
+    return a < b ? a : b;
+  }
+
+  function max256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a >= b ? a : b;
+  }
+
+  function min256(uint256 a, uint256 b) internal constant returns (uint256) {
+    return a < b ? a : b;
+  }
+
   function assert(bool assertion) internal {
     if (!assertion) throw;
   }
diff --git a/contracts/token/GrantableToken.sol b/contracts/token/GrantableToken.sol
index 712a53021..79fc328e9 100644
--- a/contracts/token/GrantableToken.sol
+++ b/contracts/token/GrantableToken.sol
@@ -67,12 +67,12 @@ contract GrantableToken is StandardToken {
     if (time < cliff) return 0;
     if (time > vesting) return tokens;
 
-    uint256 cliffTokens = safeMul(tokens, (cliff - start) / (vesting - start));
+    uint256 cliffTokens = safeMul(tokens, safeDiv(safeSub(cliff, start), safeSub(vesting, start)));
     vestedTokens = cliffTokens;
 
     uint256 vestingTokens = safeSub(tokens, cliffTokens);
 
-    vestedTokens = safeAdd(vestedTokens, vestingTokens * (time - cliff) / (vesting - start));
+    vestedTokens = safeAdd(vestedTokens, safeMul(vestingTokens, safeDiv(safeSub(time, cliff), safeSub(vesting, start))));
   }
 
   function nonVestedTokens(TokenGrant grant, uint64 time) private constant returns (uint256) {
@@ -102,12 +102,4 @@ contract GrantableToken is StandardToken {
 
     return super.transfer(_to, _value);
   }
-
-  function max64(uint64 a, uint64 b) private constant returns (uint64) {
-    return a >= b ? a : b;
-  }
-
-  function min256(uint256 a, uint256 b) private constant returns (uint256) {
-    return a < b ? a : b;
-  }
 }