Index: src/pmc/packfile.pmc
===================================================================
--- src/pmc/packfile.pmc	(revision 45332)
+++ src/pmc/packfile.pmc	(working copy)
@@ -171,12 +171,13 @@
 */
     VTABLE void set_string_native(STRING *str) {
         PackFile  * const pf  = PackFile_new(interp, 0);
-        opcode_t  * const ptr = (opcode_t *)Parrot_string_cstring(interp, str);
+        opcode_t  * const ptr = (opcode_t *)Parrot_str_to_cstring(interp, str);
         const int length      = Parrot_str_byte_length(interp, str);
         Parrot_Packfile_attributes * const attrs = PARROT_PACKFILE(SELF);
 
         if (!PackFile_unpack(interp, pf, ptr, length)) {
             PackFile_destroy(interp, pf);
+            Parrot_str_free_cstring(ptr);
             Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_MALFORMED_PACKFILE,
                                         "Can't unpack packfile.");
         }
@@ -192,6 +193,7 @@
         Parrot_unblock_GC_mark(interp);
 
         PackFile_destroy(interp, pf);
+        Parrot_str_free_cstring(ptr);
     }
 
 
@@ -250,9 +252,17 @@
         if (!Parrot_str_compare(interp, key, CONST_STRING(interp, "uuid_type")))
             return attrs->uuid_type;
 
-        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_KEY_NOT_FOUND,
-                       "Packfile: No such integer key \"%s\"",
-                       Parrot_string_cstring(interp, key));
+        const char start_buffer[] = "Packfile: No such integer key \"";
+        STRING * message =
+            Parrot_str_new(interp, start_buffer, sizeof (start_buffer));
+        STRING * const message_end = Parrot_str_new(interp, "\"", 1);
+        message = Parrot_str_append(interp, message, key);
+        message = Parrot_str_append(interp, message, message_end);
+
+        PMC * const except = Parrot_ex_build_exception(interp, NULL,
+                       EXCEPTION_KEY_NOT_FOUND, message);
+
+        Parrot_ex_throw_from_c(interp, except);
     }
 
 /*
@@ -274,9 +284,17 @@
         if (!Parrot_str_compare(interp, key, CONST_STRING(interp, "uuid")))
             return PARROT_PACKFILE(SELF)->uuid;
 
-        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_KEY_NOT_FOUND,
-                       "Packfile: No such string key \"%s\"",
-                       Parrot_string_cstring(interp, key));
+        const char start_buffer[] = "Packfile: No such string key \"";
+        STRING * message =
+            Parrot_str_new(interp, start_buffer, sizeof (start_buffer));
+        STRING * const message_end = Parrot_str_new(interp, "\"", 1);
+        message = Parrot_str_append(interp, message, key);
+        message = Parrot_str_append(interp, message, message_end);
+
+        PMC * const except = Parrot_ex_build_exception(interp, NULL,
+                       EXCEPTION_KEY_NOT_FOUND, message);
+
+        Parrot_ex_throw_from_c(interp, except);
     }
 
 
@@ -350,9 +368,18 @@
             attrs->uuid_type = value;
             return;
         }
-        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_KEY_NOT_FOUND,
-                       "Packfile: No such integer key \"%s\"",
-                       Parrot_string_cstring(interp, key));
+
+        const char start_buffer[] = "Packfile: No such integer key \"";
+        STRING * message =
+            Parrot_str_new(interp, start_buffer, sizeof (start_buffer));
+        STRING * const message_end = Parrot_str_new(interp, "\"", 1);
+        message = Parrot_str_append(interp, message, key);
+        message = Parrot_str_append(interp, message, message_end);
+
+        PMC * const except = Parrot_ex_build_exception(interp, NULL,
+                       EXCEPTION_KEY_NOT_FOUND, message);
+
+        Parrot_ex_throw_from_c(interp, except);
     }
 
 
@@ -394,9 +421,17 @@
             return;
         }
 
-        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_KEY_NOT_FOUND,
-                       "Packfile: No such string key \"%s\"",
-                       Parrot_string_cstring(interp, key));
+        const char start_buffer[] = "Packfile: No such integer key \"";
+        STRING * message =
+            Parrot_str_new(interp, start_buffer, sizeof (start_buffer));
+        STRING * const message_end = Parrot_str_new(interp, "\"", 1);
+        message = Parrot_str_append(interp, message, key);
+        message = Parrot_str_append(interp, message, message_end);
+
+        PMC * const except = Parrot_ex_build_exception(interp, NULL,
+                       EXCEPTION_KEY_NOT_FOUND, message);
+
+        Parrot_ex_throw_from_c(interp, except);
     }
 
 /*
Index: src/pmc/packfilefixupentry.pmc
===================================================================
--- src/pmc/packfilefixupentry.pmc	(revision 45332)
+++ src/pmc/packfilefixupentry.pmc	(working copy)
@@ -100,10 +100,12 @@
                 PARROT_PACKFILEFIXUPENTRY(SELF);
         PackFile_FixupEntry                  * entry =
                 mem_gc_allocate_zeroed_typed(INTERP, PackFile_FixupEntry);
-
+        const char * tempName = Parrot_str_to_cstring(interp, attrs->name);
         entry->type     = attrs->type;
-        entry->name     = strdup(Parrot_string_cstring(interp, attrs->name));
+        entry->name     = strdup(tempName);
         entry->offset   = attrs->offset;
+
+        Parrot_str_free_cstring(tempName);
         return entry;
     }