diff --git a/amount.cc b/amount.cc
index b72f9852..e0507c7c 100644
--- a/amount.cc
+++ b/amount.cc
@@ -276,11 +276,12 @@ amount_t& amount_t::operator=(const char * value)
 // assignment operator
 amount_t& amount_t::operator=(const amount_t& amt)
 {
-  if (amt.quantity)
-    _copy(amt);
-  else if (quantity)
-    _clear();
-
+  if (this != &amt) {
+    if (amt.quantity)
+      _copy(amt);
+    else if (quantity)
+      _clear();
+  }
   return *this;
 }
 
diff --git a/balance.h b/balance.h
index 7f547e8d..f88f3114 100644
--- a/balance.h
+++ b/balance.h
@@ -70,11 +70,13 @@ class balance_t
 
   // assignment operator
   balance_t& operator=(const balance_t& bal) {
-    amounts.clear();
-    for (amounts_map::const_iterator i = bal.amounts.begin();
-	 i != bal.amounts.end();
-	 i++)
-      *this += (*i).second;
+    if (this != &bal) {
+      amounts.clear();
+      for (amounts_map::const_iterator i = bal.amounts.begin();
+	   i != bal.amounts.end();
+	   i++)
+	*this += (*i).second;
+    }
     return *this;
   }
   balance_t& operator=(const amount_t& amt) {
@@ -452,15 +454,16 @@ class balance_pair_t
 
   // assignment operator
   balance_pair_t& operator=(const balance_pair_t& bal_pair) {
-    if (cost) {
-      delete cost;
-      cost = NULL;
+    if (this != &bal_pair) {
+      if (cost) {
+	delete cost;
+	cost = NULL;
+      }
+
+      quantity = bal_pair.quantity;
+      if (bal_pair.cost)
+	cost = new balance_t(*bal_pair.cost);
     }
-
-    quantity = bal_pair.quantity;
-    if (bal_pair.cost)
-      cost = new balance_t(*bal_pair.cost);
-
     return *this;
   }
   balance_pair_t& operator=(const balance_t& bal) {
diff --git a/value.cc b/value.cc
index bf235257..83307dc0 100644
--- a/value.cc
+++ b/value.cc
@@ -22,6 +22,9 @@ void value_t::destroy()
 
 value_t& value_t::operator=(const value_t& value)
 {
+  if (this == &value)
+    return *this;
+
   destroy();
   switch (value.type) {
   case BOOLEAN:
diff --git a/walk.h b/walk.h
index 238fdb78..39bde7f2 100644
--- a/walk.h
+++ b/walk.h
@@ -53,8 +53,9 @@ class compare_items {
     assert(right);
 
     value_t left_result;
-    sort_order->compute(left_result, details_t(left));
     value_t right_result;
+
+    sort_order->compute(left_result, details_t(left));
     sort_order->compute(right_result, details_t(right));
 
     return left_result < right_result;