diff --git a/examples/inject.rs b/examples/inject.rs
index c03d8d4..03d027a 100644
--- a/examples/inject.rs
+++ b/examples/inject.rs
@@ -3,6 +3,7 @@ extern crate parity_wasm;
 use std::env;
 
 use parity_wasm::elements;
+use parity_wasm::builder;
 
 pub fn inject_nop(opcodes: &mut elements::Opcodes) {
     use parity_wasm::elements::Opcode::*;
@@ -38,5 +39,19 @@ fn main() {
         }
     }
 
-    parity_wasm::serialize_to_file(&args[2], module).unwrap();
+    let mut build = builder::from_module(module);
+    let import_sig = build.push_signature(
+        builder::signature()
+            .param().i32()
+            .param().i32()
+            .return_type().i32()
+            .build_sig()
+    );
+    let build = build.import()
+        .module("env")
+        .field("log")
+        .external().func(import_sig)
+        .build();
+
+    parity_wasm::serialize_to_file(&args[2], build.build()).unwrap();
 }
\ No newline at end of file
diff --git a/src/builder/code.rs b/src/builder/code.rs
index d919f97..710a377 100644
--- a/src/builder/code.rs
+++ b/src/builder/code.rs
@@ -12,6 +12,12 @@ pub struct SignatureBuilder<F=Identity> {
     signature: elements::FunctionType,
 }
 
+impl SignatureBuilder {
+    pub fn new() -> Self {
+        SignatureBuilder::with_callback(Identity)
+    }
+}
+
 impl<F> SignatureBuilder<F> where F: Invoke<elements::FunctionType> {
     pub fn with_callback(callback: F) -> Self {
         SignatureBuilder { 
@@ -50,6 +56,10 @@ impl<F> SignatureBuilder<F> where F: Invoke<elements::FunctionType> {
     pub fn build(self) -> F::Result {
         self.callback.invoke(self.signature)
     }
+
+    pub fn build_sig(self) -> Signature {
+        Signature::Inline(self.signature)
+    }
 }
 
 impl<F> Invoke<Vec<elements::ValueType>> for SignatureBuilder<F>
@@ -298,6 +308,11 @@ pub fn signatures() -> SignaturesBuilder {
     SignaturesBuilder::new()
 }
 
+/// New signature builder
+pub fn signature() -> SignatureBuilder {
+    SignatureBuilder::new()
+}
+
 /// New builder of function (signature & body)
 pub fn function() -> FunctionBuilder {
     FunctionBuilder::new()
diff --git a/src/builder/mod.rs b/src/builder/mod.rs
index 6a2436e..06766b8 100644
--- a/src/builder/mod.rs
+++ b/src/builder/mod.rs
@@ -7,5 +7,5 @@ mod misc;
 mod import;
 
 pub use self::module::{module, from_module, ModuleBuilder};
-pub use self::code::{signatures, function};
+pub use self::code::{signatures, signature, function};
 pub use self::import::import;
\ No newline at end of file
diff --git a/src/builder/module.rs b/src/builder/module.rs
index 0eacbd7..8a7701b 100644
--- a/src/builder/module.rs
+++ b/src/builder/module.rs
@@ -123,22 +123,13 @@ impl<F> ModuleBuilder<F> where F: Invoke<elements::Module> {
     pub fn push_function(&mut self, func: code::FunctionDefinition) -> CodeLocation {
         let signature = func.signature;
         let body = func.code;
-        let module = &mut self.module;
 
-        let type_ref = match signature {
-            code::Signature::Inline(func_type) => {
-                module.types.types_mut().push(elements::Type::Function(func_type));
-                module.types.types().len() as u32 - 1
-            }
-            code::Signature::TypeReference(type_ref) => {
-                type_ref
-            }
-        };
+        let type_ref = self.resolve_type_ref(signature);
 
-        module.functions.entries_mut().push(elements::Func::new(type_ref));
-        let signature_index = module.functions.entries_mut().len() as u32 - 1;
-        module.code.bodies_mut().push(body);
-        let body_index = module.code.bodies_mut().len() as u32 - 1;
+        self.module.functions.entries_mut().push(elements::Func::new(type_ref));
+        let signature_index = self.module.functions.entries_mut().len() as u32 - 1;
+        self.module.code.bodies_mut().push(body);
+        let body_index = self.module.code.bodies_mut().len() as u32 - 1;
 
         CodeLocation {
             signature: signature_index,
@@ -146,17 +137,36 @@ impl<F> ModuleBuilder<F> where F: Invoke<elements::Module> {
         }
     }
 
+    fn resolve_type_ref(&mut self, signature: code::Signature) -> u32 {
+        match signature {
+            code::Signature::Inline(func_type) => {
+                self.module.types.types_mut().push(elements::Type::Function(func_type));
+                self.module.types.types().len() as u32 - 1
+            }
+            code::Signature::TypeReference(type_ref) => {
+                type_ref
+            }
+        }
+    }
+
+    /// Push one function signature, returning it's calling index.
+    /// Can create corresponding type in type section.
+    pub fn push_signature(&mut self, signature: code::Signature) -> u32 {
+        let type_ref = self.resolve_type_ref(signature);
+        self.module.functions.entries_mut().push(elements::Func::new(type_ref));
+        self.module.functions.entries_mut().len() as u32 - 1
+    }
+
     /// Push signatures in the module, returning corresponding indices of pushed signatures
     pub fn push_signatures(&mut self, signatures: code::SignatureBindings) -> Vec<u32> {
-        let module = &mut self.module;
         let mut result = Vec::new();
 
         // todo: maybe reuse existing types with the equal signatures
         let raw_functions: Vec<u32> = signatures.into_iter().map(|binding|
             match binding {
                 code::Signature::Inline(func_type) => {
-                    module.types.types_mut().push(elements::Type::Function(func_type));
-                    module.types.types().len() as u32 - 1
+                    self.module.types.types_mut().push(elements::Type::Function(func_type));
+                    self.module.types.types().len() as u32 - 1
                 }
                 code::Signature::TypeReference(type_ref) => {
                     type_ref
@@ -165,8 +175,8 @@ impl<F> ModuleBuilder<F> where F: Invoke<elements::Module> {
         ).collect();
 
         for function in raw_functions {
-            module.functions.entries_mut().push(elements::Func::new(function));
-            result.push(module.functions.entries_mut().len() as u32 - 1);
+            self.module.functions.entries_mut().push(elements::Func::new(function));
+            result.push(self.module.functions.entries_mut().len() as u32 - 1);
         }
 
         result