--- 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-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>)