diff --git a/src/wallet.js b/src/wallet.js
index 0d41bb2..846a5ad 100644
--- a/src/wallet.js
+++ b/src/wallet.js
@@ -1,3 +1,4 @@
+var assert = require('assert')
 var networks = require('./networks')
 var rng = require('secure-random')
 
@@ -169,7 +170,7 @@ function Wallet(seed, network) {
   }
 
   this.createTx = function(to, value, fixedFee, changeAddress) {
-    if (value <= this.dustThreshold) throw new Error("Value must be above dust threshold")
+    assert(value > this.dustThreshold, value + ' must be above dust threshold (' + this.dustThreshold + ' Satoshis)')
 
     var utxos = getCandidateOutputs(value)
     var accum = 0
@@ -198,9 +199,7 @@ function Wallet(seed, network) {
       }
     }
 
-    if (accum < subTotal) {
-      throw new Error('Not enough funds: ' + accum + ' < ' + subTotal)
-    }
+    assert(accum >= subTotal, 'Not enough funds (incl. fee): ' + accum + ' < ' + subTotal)
 
     this.sign(tx)
     return tx
diff --git a/test/wallet.js b/test/wallet.js
index ef2d152..c3b459b 100644
--- a/test/wallet.js
+++ b/test/wallet.js
@@ -546,7 +546,7 @@ describe('Wallet', function() {
 
         assert.throws(function() {
           wallet.createTx(to, value)
-        }, /Value must be above dust threshold/)
+        }, /5430 must be above dust threshold \(5430 Satoshis\)/)
       })
     })
 
@@ -556,7 +556,7 @@ describe('Wallet', function() {
 
         assert.throws(function() {
           wallet.createTx(to, value)
-        }, /Not enough funds: 1420000 < 1420001/)
+        }, /Not enough funds \(incl. fee\): 1420000 < 1420001/)
       })
     })
   })