diff --git a/src/signature-info.cpp b/src/signature-info.cpp
index 36964ac..0b3b0a1 100644
--- a/src/signature-info.cpp
+++ b/src/signature-info.cpp
@@ -60,6 +60,10 @@
 size_t
 SignatureInfo::wireEncode(EncodingImpl<TAG>& encoder) const
 {
+  if (m_type == -1) {
+    BOOST_THROW_EXCEPTION(Error("Cannot encode invalid SignatureInfo"));
+  }
+
   // SignatureInfo ::= SIGNATURE-INFO-TLV TLV-LENGTH
   //                     SignatureType
   //                     KeyLocator?
@@ -114,15 +118,15 @@
 
   Block::element_const_iterator it = m_wire.elements_begin();
 
-  // the first block must be SignatureType
+  // the first sub-element must be SignatureType
   if (it != m_wire.elements_end() && it->type() == tlv::SignatureType) {
-    m_type = readNonNegativeInteger(*it);
+    m_type = readNonNegativeIntegerAs<int32_t>(*it);
     ++it;
   }
   else
     BOOST_THROW_EXCEPTION(Error("Missing SignatureType in SignatureInfo"));
 
-  // the second block could be KeyLocator
+  // the second sub-element could be KeyLocator
   if (it != m_wire.elements_end() && it->type() == tlv::KeyLocator) {
     m_keyLocator.wireDecode(*it);
     m_hasKeyLocator = true;
diff --git a/src/signature.cpp b/src/signature.cpp
index 3683449..4ac9d59 100644
--- a/src/signature.cpp
+++ b/src/signature.cpp
@@ -40,6 +40,15 @@
 {
 }
 
+tlv::SignatureTypeValue
+Signature::getType() const
+{
+  if (!*this) {
+    BOOST_THROW_EXCEPTION(Error("Signature is invalid"));
+  }
+  return static_cast<tlv::SignatureTypeValue>(m_info.getSignatureType());
+}
+
 void
 Signature::setInfo(const Block& info)
 {
@@ -55,4 +64,10 @@
   m_value = value;
 }
 
+bool
+operator==(const Signature& lhs, const Signature& rhs)
+{
+  return lhs.getSignatureInfo() == rhs.getSignatureInfo() && lhs.getValue() == rhs.getValue();
+}
+
 } // namespace ndn
diff --git a/src/signature.hpp b/src/signature.hpp
index 315d061..1af7885 100644
--- a/src/signature.hpp
+++ b/src/signature.hpp
@@ -109,12 +109,10 @@
 
 public: // SignatureInfo fields
   /** @brief Get SignatureType
+   *  @throw Error signature is invalid
    */
-  uint32_t
-  getType() const
-  {
-    return m_info.getSignatureType();
-  }
+  tlv::SignatureTypeValue
+  getType() const;
 
   /** @brief Check if KeyLocator exists in SignatureInfo
    */
@@ -157,11 +155,8 @@
   mutable Block m_value;
 };
 
-inline bool
-operator==(const Signature& lhs, const Signature& rhs)
-{
-  return lhs.getInfo() == rhs.getInfo() && lhs.getValue() == rhs.getValue();
-}
+bool
+operator==(const Signature& lhs, const Signature& rhs);
 
 inline bool
 operator!=(const Signature& lhs, const Signature& rhs)