--- a/src/c-ffi.c
+++ b/src/c-ffi.c
@@ -347,7 +347,11 @@
     }
     sa = SCM_SLOT_ACCESSOR(SCM_CDR(p));
     if (0 <= sa->slotNumber) {
+#if !defined(GAUCHE_API_VERSION) || GAUCHE_API_VERSION < 98
         return SCM_FFI_TYPE_DATA(Scm_InstanceSlotRef(ctype, sa->slotNumber));
+#else
+        return SCM_FFI_TYPE_DATA(Scm_InstanceSlotRef(ctype, sa->slotNumber, SCM_UNBOUND));
+#endif
     } else {
         Scm_Error("wrong slot number: %d", sa->slotNumber);
     }
--- a/src/c-lex.c
+++ b/src/c-lex.c
@@ -992,11 +992,6 @@
     SCM_RETURN(Scm_MakeInteger(v));
 }
 
-ScmObj Scm_ReadStringLiteral()
-{
-    SCM_RETURN(read_string_literal());
-}
-
 ScmObj Scm_ReadCharacterConstant()
 {
     SCM_RETURN(read_character_constant());
--- a/src/c-lex.h
+++ b/src/c-lex.h
@@ -78,7 +78,6 @@
 extern ScmObj Scm_IsForceIdentifierSet(ScmObj v);
 extern ScmObj Scm_ReadIdentifier(ScmObj l);
 extern ScmObj Scm_ReadOperator(ScmObj c);
-extern ScmObj Scm_ReadStringLiteral();
 extern ScmObj Scm_ReadCharacterConstant();
 extern ScmObj Scm_ReadOctalOrFlonum(ScmObj l);
 extern ScmObj Scm_ReadDecimal(ScmObj l);
--- a/src/c-lexlib.stub
+++ b/src/c-lexlib.stub
@@ -40,7 +40,11 @@
         "if (nptr == endptr) {"
         "    SCM_RETURN(SCM_FALSE);"
         "} else {"
+        "#if !defined(GAUCHE_API_VERSION) || GAUCHE_API_VERSION < 98"
         "    SCM_RETURN(Scm_MakeInteger64((ScmInt64) v));"
+        "#else"
+        "    SCM_RETURN(Scm_MakeInteger64((int64_t) v));"
+        "#endif"
         "}"))
 
 (define-cproc strtod (nptr::<const-cstring>)
@@ -136,9 +140,6 @@
 (define-cproc read-operator (c)
   (call "Scm_ReadOperator"))
 
-(define-cproc read-string-literal ()
-  (call "Scm_ReadStringLiteral"))
-
 (define-cproc read-character-constant ()
   (call "Scm_ReadCharacterConstant"))