diff --git a/src/lib.rs b/src/lib.rs
index 9100e08..7103cf1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,7 +10,6 @@ extern crate byteorder;
 
 use std::fmt;
 use std::error;
-use parity_wasm::elements::{FunctionType, ValueType};
 
 /// Internal interpreter error.
 #[derive(Debug)]
@@ -98,32 +97,7 @@ impl From<::common::stack::Error> for Error {
 	}
 }
 
-#[derive(Debug, Clone, PartialEq)]
-pub struct Signature {
-	func_type: FunctionType,
-}
-
-impl Signature {
-	pub fn new(params: &[ValueType], return_type: Option<ValueType>) -> Signature {
-		Signature {
-			func_type: FunctionType::new(params.to_vec(), return_type),
-		}
-	}
-
-	pub fn params(&self) -> &[ValueType] {
-		self.func_type.params()
-	}
-
-	pub fn return_type(&self) -> Option<ValueType> {
-		self.func_type.return_type()
-	}
-}
-
-impl From<FunctionType> for Signature {
-	fn from(func_type: FunctionType) -> Signature {
-		Signature { func_type }
-	}
-}
+use types::Signature;
 
 mod validation;
 mod common;
@@ -136,6 +110,7 @@ mod host;
 mod imports;
 mod global;
 mod func;
+mod types;
 
 #[cfg(test)]
 mod tests;
diff --git a/src/types.rs b/src/types.rs
new file mode 100644
index 0000000..5fefceb
--- /dev/null
+++ b/src/types.rs
@@ -0,0 +1,28 @@
+use parity_wasm::elements::{FunctionType, ValueType};
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Signature {
+	func_type: FunctionType,
+}
+
+impl Signature {
+	pub fn new(params: &[ValueType], return_type: Option<ValueType>) -> Signature {
+		Signature {
+			func_type: FunctionType::new(params.to_vec(), return_type),
+		}
+	}
+
+	pub fn params(&self) -> &[ValueType] {
+		self.func_type.params()
+	}
+
+	pub fn return_type(&self) -> Option<ValueType> {
+		self.func_type.return_type()
+	}
+}
+
+impl From<FunctionType> for Signature {
+	fn from(func_type: FunctionType) -> Signature {
+		Signature { func_type }
+	}
+}