diff --git a/Foundation/CPDecimal.j b/Foundation/CPDecimal.j
index a38e556bb..15d2f817d 100644
--- a/Foundation/CPDecimal.j
+++ b/Foundation/CPDecimal.j
@@ -108,7 +108,7 @@ function CPDecimalMakeWithString(string, locale)
     // Regexp solution as found in JSON spec, with working regexp (I added groupings)
     // Test here: http://www.regexplanet.com/simple/index.html
     // Info from: http://stackoverflow.com/questions/638565/parsing-scientific-notation-sensibly
-    // ([+\-]?)((?:0|[1-9]\d*))  - integer part, cant have leading zeros
+    // ([+\-]?)((?:0|[0-9]\d*))  - integer part, can have leading zeros (follows Cocoa behaviour)
     //  (?:\.(\d*))?           - optional decimal part plus number in group
     //  (?:[eE]([+\-]?)(\d+))?   - optional exponent part plus number in group
     // group 0: string, 1: sign, 2: integer, 3: decimal, 4: exponent sign, 5: exponent
@@ -116,7 +116,7 @@ function CPDecimalMakeWithString(string, locale)
     // Note: this doesn't accept .01 for example, should it?
     // If yes simply add '?' after integer part group, i.e. ([+\-]?)((?:0|[1-9]\d*)?)
     // Note: now it accept .01 style.
-    var matches = string.match(/^([+\-]?)((?:0|[1-9]\d*)?)(?:\.(\d*))?(?:[eE]([+\-]?)(\d+))?$/);
+    var matches = string.match(/^([+\-]?)((?:0|[0-9]\d*)?)(?:\.(\d*))?(?:[eE]([+\-]?)(\d+))?$/);
 
     if (!matches)
         return CPDecimalMakeNaN();
diff --git a/Tests/Foundation/CPDecimalNumberTest.j b/Tests/Foundation/CPDecimalNumberTest.j
index 724953039..c85873245 100644
--- a/Tests/Foundation/CPDecimalNumberTest.j
+++ b/Tests/Foundation/CPDecimalNumberTest.j
@@ -130,6 +130,9 @@
     [self assert:[0] equals:dcm._mantissa message:"zero: - mantissa"];
     [self assert:NO equals:dcm._isNegative message:"zero: - sign"];
 
+    // this is Cocoa behaviour -- convert a decimal number with a leading zero to a number.
+    dcmn = [[CPDecimalNumber alloc] initWithString:@"0123"];
+    [self assertTrue:[dcmn isEqualToNumber:123]];
 
     // misc
     // decimalValue <- if it hasnt been working so far, you would know.
@@ -147,14 +150,11 @@
     dcmn = [[CPDecimalNumber alloc] initWithString:@"foo"];
     [self assert:CPOrderedSame equals:[dcmn compare:[CPDecimalNumber notANumber]] message:"initWithString: 2 overflow should return NaN"];
 
-    dcmn = [[CPDecimalNumber alloc] initWithString:@"0123"];
+    dcmn = [[CPDecimalNumber alloc] initWithString:@"1e200"];
     [self assert:CPOrderedSame equals:[dcmn compare:[CPDecimalNumber notANumber]] message:"initWithString: 3 overflow should return NaN"];
 
-    dcmn = [[CPDecimalNumber alloc] initWithString:@"1e200"];
-    [self assert:CPOrderedSame equals:[dcmn compare:[CPDecimalNumber notANumber]] message:"initWithString: 4 overflow should return NaN"];
-
     dcmn = [[CPDecimalNumber alloc] initWithString:@"12312e-23421"];
-    [self assert:CPOrderedSame equals:[dcmn compare:[CPDecimalNumber notANumber]] message:"initWithString: 5 overflow should return NaN"];
+    [self assert:CPOrderedSame equals:[dcmn compare:[CPDecimalNumber notANumber]] message:"initWithString: 4 overflow should return NaN"];
 }
 
 - (void)testAdd
diff --git a/Tests/Foundation/CPDecimalTest.j b/Tests/Foundation/CPDecimalTest.j
index 6ba4c5fb1..7f88d8c14 100644
--- a/Tests/Foundation/CPDecimalTest.j
+++ b/Tests/Foundation/CPDecimalTest.j
@@ -68,7 +68,7 @@
     [self assert:NO equals:dcm._isNaN message:"CPDecimalMakeWithString() Tf4: NaN is incorrectly set"];
 
     dcm = CPDecimalMakeWithString(@"000000000000000000");
-    [self assertTrue:dcm._isNaN message:"CPDecimalMakeWithString() Tf5: Should be invalid"];
+    [self assertFalse:dcm._isNaN message:"CPDecimalMakeWithString() Tf5: Should be valid"];
 
     // too large return NaN
     dcm = CPDecimalMakeWithString(@"111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111");
@@ -95,10 +95,12 @@
     [self assertTrue:dcm._isNaN message:"CPDecimalMakeWithString() Ti7: catch of invalid number string. Should return NaN"];
     dcm = CPDecimalMakeWithString(@"123ee");
     [self assertTrue:dcm._isNaN message:"CPDecimalMakeWithString() Ti8: catch of invalid number string. Should return NaN"];
+
+    // this behaviour has changed to match Cocoa. Making a decimal with a leading zero should return the decimal.
     dcm = CPDecimalMakeWithString(@"0001");
-    [self assertTrue:dcm._isNaN message:"CPDecimalMakeWithString() Ti9: catch of invalid number string. Should return NaN"];
+    [self assertFalse:dcm._isNaN message:"CPDecimalMakeWithString() Ti9: Numbers with leading zeros are valid numbers. Expected False when evaluating against NaN, got True."];
     dcm = CPDecimalMakeWithString(@"-0001");
-    [self assertTrue:dcm._isNaN message:"CPDecimalMakeWithString() Ti10: catch of invalid number string. Should return NaN"];
+    [self assertFalse:dcm._isNaN message:"CPDecimalMakeWithString() Ti10: Numbers with leading zeros are valid numbers. Expected False when evaluating against NaN, got True."];
 
     //test make with parts
     dcm = CPDecimalMakeWithParts(10127658, 2);