--- a/financepy/models/merton_firm_mkt.py
+++ b/financepy/models/merton_firm_mkt.py
@@ -158,12 +158,17 @@
             else:
                 argtuple += (self._r[0],)
 
+            # Normalize monetary amounts by the debt face before calibration.
+            monetary_scale = argtuple[2]
+            argtuple = (argtuple[0] / monetary_scale, argtuple[1],
+                        1.0, argtuple[3], argtuple[4])
+
             # I initialise asset value and vol to equity value and vol
             x0 = np.array([argtuple[0], argtuple[1]])
 
             result = optimize.minimize(_fobj, x0, args=argtuple, tol=1e-9)
 
-            self._a.append(result.x[0])
+            self._a.append(result.x[0] * monetary_scale)
             self._va.append(result.x[1])
 
         self._a = np.array(self._a)