diff --git a/src/ast.hpp b/src/ast.hpp
index 7ea0557d03..be9dc0e34a 100644
--- a/src/ast.hpp
+++ b/src/ast.hpp
@@ -1703,16 +1703,16 @@ namespace Sass {
   // Interpolated strings. Meant to be reduced to flat strings during the
   // evaluation phase.
   ///////////////////////////////////////////////////////////////////////
-  class String_Schema : public String, public Vectorized<Expression_Obj> {
+  class String_Schema : public String, public Vectorized<PreValue_Obj> {
     ADD_PROPERTY(bool, css)
     size_t hash_;
   public:
     String_Schema(ParserState pstate, size_t size = 0, bool css = true)
-    : String(pstate), Vectorized<Expression_Obj>(size), css_(css), hash_(0)
+    : String(pstate), Vectorized<PreValue_Obj>(size), css_(css), hash_(0)
     { concrete_type(STRING); }
     String_Schema(const String_Schema* ptr)
     : String(ptr),
-      Vectorized<Expression_Obj>(*ptr),
+      Vectorized<PreValue_Obj>(*ptr),
       css_(ptr->css_),
       hash_(ptr->hash_)
     { concrete_type(STRING); }
diff --git a/src/eval.cpp b/src/eval.cpp
index 77f9480046..0b09ede23e 100644
--- a/src/eval.cpp
+++ b/src/eval.cpp
@@ -663,9 +663,9 @@ namespace Sass {
                                                     b->op(), s_l->last(), b->right());
         bin_ex->is_delayed(b->left()->is_delayed() || b->right()->is_delayed()); // unverified
         for (size_t i = 0; i < s_l->length() - 1; ++i) {
-          ret_schema->append(s_l->at(i)->perform(this));
+          ret_schema->append(Cast<PreValue>(s_l->at(i)->perform(this)));
         }
-        ret_schema->append(bin_ex->perform(this));
+        ret_schema->append(Cast<PreValue>(bin_ex->perform(this)));
         return ret_schema->perform(this);
       }
     }
@@ -676,9 +676,9 @@ namespace Sass {
         Binary_Expression_Obj bin_ex = SASS_MEMORY_NEW(Binary_Expression, b->pstate(),
                                                     b->op(), b->left(), s_r->first());
         bin_ex->is_delayed(b->left()->is_delayed() || b->right()->is_delayed()); // verified
-        ret_schema->append(bin_ex->perform(this));
+        ret_schema->append(Cast<PreValue>(bin_ex->perform(this)));
         for (size_t i = 1; i < s_r->length(); ++i) {
-          ret_schema->append(s_r->at(i)->perform(this));
+          ret_schema->append(Cast<PreValue>(s_r->at(i)->perform(this)));
         }
         return ret_schema->perform(this);
       }