diff --git a/fortran/src/include/primes.f90 b/fortran/src/include/primes.f90
index 95c9517b..835ad51f 100644
--- a/fortran/src/include/primes.f90
+++ b/fortran/src/include/primes.f90
@@ -59,8 +59,8 @@ subroutine expand_sieve(potential_n)
         do i = 1, new_size
             is_prime(i) = 2**bits_per_int - 1
         end do
-        call clear_prime_bit(0)
-        call clear_prime_bit(1)
+        call clear_prime_bit(0_i18t)
+        call clear_prime_bit(1_i18t)
         call sieve_up_to(new_n)
         current_n = new_n
     end subroutine expand_sieve
@@ -72,7 +72,7 @@ subroutine clear_prime_bit(num)
         i = (num / bits_per_int) + 1
         b = mod(num, bits_per_int)
         print *, "Translating bit #", num, "to", i, b
-        is_prime(i) = iand(is_prime(i), ieor(-1, 2**b))
+        is_prime(i) = iand(is_prime(i), ieor(-1_i18t, 2**b))
     end subroutine clear_prime_bit
 
     ! Function to check if a bit is set
diff --git a/fortran/src/p0007.f90 b/fortran/src/p0007.f90
index 41a8d958..abc994c0 100644
--- a/fortran/src/p0007.f90
+++ b/fortran/src/p0007.f90
@@ -8,10 +8,11 @@
 ! What is the 10 001st prime number?
 
 module Problem0007
+    use constants
     use primes
     implicit none
 contains
-    integer function p0007() result(answer)
+    integer(i18t) function p0007() result(answer)
         integer :: i
 
         answer = 1