diff --git a/flang/module/__fortran_ieee_exceptions.f90 b/flang/module/__fortran_ieee_exceptions.f90
--- a/flang/module/__fortran_ieee_exceptions.f90
+++ b/flang/module/__fortran_ieee_exceptions.f90
@@ -124,13 +124,13 @@
   end interface
 
 #define IEEE_SUPPORT_FLAG_R(XKIND) \
-  logical function ieee_support_flag_a##XKIND(flag, x); \
+  pure logical function ieee_support_flag_a##XKIND(flag, x); \
     import ieee_flag_type; \
     type(ieee_flag_type), intent(in) :: flag; \
     real(XKIND), intent(in) :: x(..); \
   end function ieee_support_flag_a##XKIND;
   interface ieee_support_flag
-    logical function ieee_support_flag(flag)
+    pure logical function ieee_support_flag(flag)
       import ieee_flag_type
       type(ieee_flag_type), intent(in) :: flag
     end function ieee_support_flag
diff --git a/flang/module/ieee_arithmetic.f90 b/flang/module/ieee_arithmetic.f90
--- a/flang/module/ieee_arithmetic.f90
+++ b/flang/module/ieee_arithmetic.f90
@@ -514,7 +514,7 @@
     real(XKIND), intent(in) :: x(..); \
   end function ieee_support_rounding_a##XKIND;
   interface ieee_support_rounding
-    logical function ieee_support_rounding(round_value)
+    pure logical function ieee_support_rounding(round_value)
       import ieee_round_type
       type(ieee_round_type), intent(in) :: round_value
     end function ieee_support_rounding