diff --git a/libs/cassowary/cassowary/ClReader.h b/libs/cassowary/cassowary/ClReader.h
index 59369d6ac2..4eef907759 100644
--- a/libs/cassowary/cassowary/ClReader.h
+++ b/libs/cassowary/cassowary/ClReader.h
@@ -35,6 +35,7 @@ class ClConstraint;
 
 class ClVarLookupFunction : public std::unary_function<const string &,ClVariable *> {
 public:
+  virtual ~ClVarLookupFunction () {};
   virtual ClVariable *operator()(const string &) const { return &clvNil; }
 };
 
@@ -50,6 +51,8 @@ public:
   ClVarLookupInMap(StringToVarMap *pmapVars, bool fAutoCreate) 
       : _pmapVars(pmapVars), _fAutoCreate(fAutoCreate) { }
 
+  virtual ~ClVarLookupInMap () {};
+
   ClVariable *operator()(const string &str) const
     { 
       if (!_pmapVars)
diff --git a/libs/cassowary/cassowary/ClVariable.h b/libs/cassowary/cassowary/ClVariable.h
index 03814e5ef2..b046247c67 100644
--- a/libs/cassowary/cassowary/ClVariable.h
+++ b/libs/cassowary/cassowary/ClVariable.h
@@ -56,6 +56,9 @@ public:
       : pclv(pcfv) 
     { if (pmapStrPclv) { (*pmapStrPclv)[pcfv->Name()] = *this; } }
 
+  // Destructor
+  virtual ~ClVariable() {};
+
   /// permit ClVariables to be used as pointers to pclvs
   ClAbstractVariable *operator->() { return pclv; }
   const ClAbstractVariable *operator->() const { return pclv; }
diff --git a/libs/soundtouch/FIFOSamplePipe.h b/libs/soundtouch/FIFOSamplePipe.h
index 9e33363b00..d2d54d5274 100644
--- a/libs/soundtouch/FIFOSamplePipe.h
+++ b/libs/soundtouch/FIFOSamplePipe.h
@@ -59,6 +59,7 @@ namespace soundtouch
 class FIFOSamplePipe
 {
 public:
+    virtual ~FIFOSamplePipe () {};
     /// Returns a pointer to the beginning of the output samples. 
     /// This function is provided for accessing the output samples directly. 
     /// Please be careful for not to corrupt the book-keeping!