diff --git a/lang/funcs/cidr.go b/lang/funcs/cidr.go
index 024c28a851..3a20ec282e 100644
--- a/lang/funcs/cidr.go
+++ b/lang/funcs/cidr.go
@@ -97,10 +97,6 @@ var CidrSubnetFunc = function.New(&function.Spec{
 			return cty.UnknownVal(cty.String), fmt.Errorf("invalid CIDR expression: %s", err)
 		}
 
-		if newbits > 64 {
-			return cty.UnknownVal(cty.String), fmt.Errorf("may not extend prefix by more than 64 bits")
-		}
-
 		newNetwork, err := cidr.SubnetBig(network, newbits, netnum)
 		if err != nil {
 			return cty.UnknownVal(cty.String), err
diff --git a/lang/funcs/cidr_test.go b/lang/funcs/cidr_test.go
index b80ad8cbdd..4bed530cba 100644
--- a/lang/funcs/cidr_test.go
+++ b/lang/funcs/cidr_test.go
@@ -56,6 +56,12 @@ func TestCidrHost(t *testing.T) {
 			cty.UnknownVal(cty.String),
 			true, // can't have an octet >255
 		},
+		{ // fractions are Not Ok
+			cty.StringVal("10.256.0.0/8"),
+			cty.NumberFloatVal(.75),
+			cty.UnknownVal(cty.String),
+			true,
+		},
 	}
 
 	for _, test := range tests {
@@ -183,21 +189,28 @@ func TestCidrSubnet(t *testing.T) {
 			cty.StringVal("192.168.0.0/168"),
 			cty.NumberIntVal(2),
 			cty.NumberIntVal(16),
-			cty.StringVal("fe80:0:0:6::/64"),
+			cty.UnknownVal(cty.String),
 			true,
 		},
 		{ // not a valid CIDR mask
 			cty.StringVal("not-a-cidr"),
 			cty.NumberIntVal(4),
 			cty.NumberIntVal(6),
-			cty.StringVal("fe80:0:0:6::/64"),
+			cty.UnknownVal(cty.String),
 			true,
 		},
 		{ // can't have an octet >255
 			cty.StringVal("10.256.0.0/8"),
 			cty.NumberIntVal(4),
 			cty.NumberIntVal(6),
-			cty.StringVal("fe80:0:0:6::/64"),
+			cty.UnknownVal(cty.String),
+			true,
+		},
+		{ // fractions are Not Ok
+			cty.StringVal("10.256.0.0/8"),
+			cty.NumberFloatVal(2 / 3),
+			cty.NumberFloatVal(.75),
+			cty.UnknownVal(cty.String),
 			true,
 		},
 	}