diff --git a/src/ripple/types/api/UInt128.h b/src/ripple/types/api/UInt128.h
index 84aac2290..569fc3f7b 100644
--- a/src/ripple/types/api/UInt128.h
+++ b/src/ripple/types/api/UInt128.h
@@ -31,6 +31,12 @@ namespace ripple {
 
 class uint128 : public base_uint128
 {
+private:
+    uint128 (value_type const* ptr)
+    {
+        memcpy (pn, ptr, bytes);
+    }
+
 public:
     typedef base_uint128 basetype;
 
@@ -52,15 +58,6 @@ public:
         return *this;
     }
 
-    // VFALCO NOTE This looks dangerous and wouldn't be obvious at call
-    //             sites what is being performed here.
-    //
-    explicit uint128 (const base_uint256& b)
-    {
-        for (int i = 0; i < WIDTH; i++)
-            pn[i] = b.pn[i];
-    }
-
     explicit uint128 (Blob const& vch)
     {
         if (vch.size () == size ())
@@ -69,6 +66,10 @@ public:
             zero ();
     }
 
+    static uint128 low128(base_uint256 const& b)
+    {
+        return uint128 (b.data());
+    }
 };
 
 }
diff --git a/src/ripple/types/api/UInt160.h b/src/ripple/types/api/UInt160.h
index 2fdcd6d19..12f411c56 100644
--- a/src/ripple/types/api/UInt160.h
+++ b/src/ripple/types/api/UInt160.h
@@ -53,7 +53,7 @@ public:
         return *this;
     }
 
-    uint160 (std::uint64_t b)
+    explicit uint160 (std::uint64_t b)
     {
         *this = b;
     }
diff --git a/src/ripple/types/api/UInt256.h b/src/ripple/types/api/UInt256.h
index 3e725b351..d84bf476a 100644
--- a/src/ripple/types/api/UInt256.h
+++ b/src/ripple/types/api/UInt256.h
@@ -56,7 +56,7 @@ public:
         return *this;
     }
 
-    uint256 (std::uint64_t b)
+    explicit uint256 (std::uint64_t b)
     {
         *this = b;
     }
diff --git a/src/ripple/types/api/base_uint.h b/src/ripple/types/api/base_uint.h
index 8a39301a5..7413e71cb 100644
--- a/src/ripple/types/api/base_uint.h
+++ b/src/ripple/types/api/base_uint.h
@@ -50,6 +50,9 @@ inline int Testuint256AdHoc (std::vector<std::string> vArg);
 template<unsigned int BITS>
 class base_uint
 {
+    static_assert ((BITS % 32) == 0,
+        "The length of a base_uint must be a multiple of 32.");
+
 protected:
     enum { WIDTH = BITS / 32 };
 
@@ -129,9 +132,6 @@ protected:
     */
     base_uint (void const* data, FromVoid)
     {
-        // BITS must be a multiple of 32
-        static_bassert ((BITS % 32) == 0);
-
         memcpy (&pn [0], data, BITS / 8);
     }
 public:
diff --git a/src/ripple_app/contracts/ScriptData.h b/src/ripple_app/contracts/ScriptData.h
index 9f87f973d..703afe361 100644
--- a/src/ripple_app/contracts/ScriptData.h
+++ b/src/ripple_app/contracts/ScriptData.h
@@ -70,7 +70,7 @@ public:
     }
     virtual uint160 getUint160 ()
     {
-        return (0);
+        return uint160(0);
     }
 
     //virtual bool isCurrency(){ return(false); }
diff --git a/src/ripple_data/crypto/CKeyDeterministic.cpp b/src/ripple_data/crypto/CKeyDeterministic.cpp
index 0253b8815..ce00c97fe 100644
--- a/src/ripple_data/crypto/CKeyDeterministic.cpp
+++ b/src/ripple_data/crypto/CKeyDeterministic.cpp
@@ -30,7 +30,7 @@ uint128 CKey::PassPhraseToKey (const std::string& passPhrase)
 
     s.addRaw (passPhrase);
     uint256 hash256 = s.getSHA512Half ();
-    uint128 ret (hash256);
+    uint128 ret (uint128::low128(hash256));
 
     s.secureErase ();
 
diff --git a/src/ripple_data/protocol/STAmount.cpp b/src/ripple_data/protocol/STAmount.cpp
index 82936bf67..87addd121 100644
--- a/src/ripple_data/protocol/STAmount.cpp
+++ b/src/ripple_data/protocol/STAmount.cpp
@@ -765,19 +765,23 @@ STAmount& STAmount::operator= (std::uint64_t v)
 
 STAmount& STAmount::operator+= (std::uint64_t v)
 {
-    if (mIsNative)
-        setSNValue (getSNValue () + static_cast<std::int64_t> (v));
-    else *this += STAmount (mCurrency, v);
+    assert (mIsNative);
 
+    if (!mIsNative)
+        throw std::runtime_error ("not native");
+
+    setSNValue (getSNValue () + static_cast<std::int64_t> (v));
     return *this;
 }
 
 STAmount& STAmount::operator-= (std::uint64_t v)
 {
-    if (mIsNative)
-        setSNValue (getSNValue () - static_cast<std::int64_t> (v));
-    else *this -= STAmount (mCurrency, v);
+    assert (mIsNative);
 
+    if (!mIsNative)
+        throw std::runtime_error ("not native");
+
+    setSNValue (getSNValue () - static_cast<std::int64_t> (v));
     return *this;
 }