1 files changed, 11 insertions, 4 deletions
diff --git a/balance.h b/balance.h
index 83cf66b1..8f953fd5 100644
--- a/balance.h
+++ b/balance.h
@@ -97,10 +97,14 @@ class balance_t
   }
   balance_t& operator-=(const amount_t& amt) {
     amounts_map::iterator i = amounts.find(&amt.commodity());
-    if (i != amounts.end())
+    if (i != amounts.end()) {
       (*i).second -= amt;
-    else if (amt)
+      if (! (*i).second)
+	amounts.erase(&amt.commodity());
+    }
+    else if (amt) {
       amounts.insert(amounts_pair(&amt.commodity(), - amt));
+    }
     return *this;
   }
   template <typename T>
@@ -147,7 +151,10 @@ class balance_t
   balance_t& operator*=(const amount_t& amt) {
     // Multiplying by the null commodity causes all amounts to be
     // increased by the same factor.
-    if (amt.commodity().symbol.empty()) {
+    if (! amt) {
+      amounts.clear();
+    }
+    else if (! amt.commodity()) {
       for (amounts_map::iterator i = amounts.begin();
 	   i != amounts.end();
 	   i++)
@@ -172,7 +179,7 @@ class balance_t
   balance_t& operator/=(const amount_t& amt) {
     // Dividing by the null commodity causes all amounts to be
     // increased by the same factor.
-    if (amt.commodity().symbol.empty()) {
+    if (! amt.commodity()) {
       for (amounts_map::iterator i = amounts.begin();
 	   i != amounts.end();
 	   i++)