diff --git a/src/lib/opaque-holder.hpp b/src/lib/opaque-holder.hpp
index 646c24b45..d19ecfcc8 100644
--- a/src/lib/opaque-holder.hpp
+++ b/src/lib/opaque-holder.hpp
@@ -73,6 +73,7 @@
 #include "lib/util.hpp"
 
 #include <boost/noncopyable.hpp>
+#include <boost/static_assert.hpp>
 
 
 namespace lib {
@@ -266,7 +267,8 @@ namespace lib {
           explicit
           Buff (SUB const& obj)
             {
-              REQUIRE (siz >= sizeof(SUB));
+              BOOST_STATIC_ASSERT (siz >= sizeof(SUB));
+              
               new(Buffer::ptr()) SUB (obj);
             }
           
@@ -613,6 +615,8 @@ namespace lib {
       void
       placeDefault()
         {
+          BOOST_STATIC_ASSERT (siz >= sizeof(DEFAULT));
+          
           new(&buf_) DEFAULT();
         }
       
@@ -640,13 +644,14 @@ namespace lib {
           destroy();                         \
           try                                 \
             {                                  \
-              REQUIRE (siz >= sizeof(TY));      \
-              return *new(&buf_) _CTOR_CALL_;    \
-            }                                     \
-          catch (...)                              \
-            {                                       \
-              placeDefault();                        \
-              throw;                                  \
+              BOOST_STATIC_ASSERT (siz >= sizeof(TY));\
+                                                 \
+              return *new(&buf_) _CTOR_CALL_;     \
+            }                                      \
+          catch (...)                               \
+            {                                        \
+              placeDefault();                         \
+              throw;                                   \
             }
       
       
diff --git a/src/lib/polymorphic-value.hpp b/src/lib/polymorphic-value.hpp
index a9b92bc5e..2213a67a3 100644
--- a/src/lib/polymorphic-value.hpp
+++ b/src/lib/polymorphic-value.hpp
@@ -146,6 +146,7 @@
 #include "lib/meta/duck-detector.hpp"
 
 #include <boost/utility/enable_if.hpp>
+#include <boost/static_assert.hpp>
 
 
 namespace lib {
@@ -384,7 +385,8 @@ namespace lib {
       template<class IMP>
       PolymorphicValue (IMP*)
         {
-          REQUIRE (siz >= sizeof(IMP));
+          BOOST_STATIC_ASSERT (siz >= sizeof(IMP));
+          
           new(&buf_) IMP();
         }
       
diff --git a/src/proc/mobject/output-designation.hpp b/src/proc/mobject/output-designation.hpp
index d9b24dc6e..ab5c3ca55 100644
--- a/src/proc/mobject/output-designation.hpp
+++ b/src/proc/mobject/output-designation.hpp
@@ -103,10 +103,12 @@ namespace mobject {
         };
       
     private:
-      enum {
-        SPEC_SIZ = mp::maxSize<
+      enum
+        { VTABLE   = sizeof(size_t)
+        , SPEC_SIZ = VTABLE
+                   + mp::maxSize<
                        mp::Types< PID, lumiera_uid, uint>::List>::value 
-      };
+        };
       typedef lib::OpaqueHolder<TargetSpec, SPEC_SIZ> SpecBuff;