diff --git a/C/arith0.c b/C/arith0.c
index 26e11db2c..e93e6c238 100644
--- a/C/arith0.c
+++ b/C/arith0.c
@@ -139,7 +139,7 @@ eval0(Int fi) {
       P = (yamop *)FAILCODE;
       RERROR();
 #else
-      if (yap_flags[LANGUAGE_MODE_FLAG] == 1) {/* iso */
+      if (isoLanguageFlag()) {/* iso */
 	Yap_ArithError(TYPE_ERROR_EVALUABLE, TermNil, "evaluating infinity");
 	P = (yamop *)FAILCODE;
 	RERROR();
@@ -154,7 +154,7 @@ eval0(Int fi) {
       Yap_ArithError(TYPE_ERROR_EVALUABLE, TermNil, "evaluating infinity");
       RERROR();
 #else
-      if (yap_flags[LANGUAGE_MODE_FLAG] == 1) {/* iso */
+      if (isoLanguageFlag()) {/* iso */
 	Yap_ArithError(TYPE_ERROR_EVALUABLE, TermNil, "evaluating not-a-number");
 	RERROR();
       } else {
diff --git a/C/arith1.c b/C/arith1.c
index b698c2ad0..1519bf63f 100644
--- a/C/arith1.c
+++ b/C/arith1.c
@@ -841,7 +841,7 @@ eval1(Int fi, Term t USES_REGS) {
   case op_ffracp:
     switch (ETypeOfTerm(t)) {
     case long_int_e:
-      if (yap_flags[LANGUAGE_MODE_FLAG] == 1) { /* iso */
+      if (isoLanguageFlag()) { /* iso */
 	return Yap_ArithError(TYPE_ERROR_FLOAT, t, "X is float_fractional_part(%f)", IntegerOfTerm(t));
       } else {
 	RFLOAT(0.0);