diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4a0add2e0..7f43fa512 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -78,6 +78,7 @@ Moreover, it generates a new file `seedname_band.labelinfo.dat` with information
 
 - Fix berry_task check for morb, and add check for kpoint_path block in parameters [[#258]](https://github.com/wannier-developers/wannier90/pull/258)
 
+- Use 64 bit integer in io_wallclocktime [[#266]](https://github.com/wannier-developers/wannier90/pull/266)
 
 
 
diff --git a/src/constants.F90 b/src/constants.F90
index 604c0363e..8b9a98043 100644
--- a/src/constants.F90
+++ b/src/constants.F90
@@ -29,6 +29,8 @@ module w90_constants
   private
 
   !~~ GENERIC CONSTANTS ~~!
+  integer, parameter, public          :: i64 = selected_int_kind(15)
+  !! 64bit integer
 !aam_2012-04-11; fix to run on MacBook Air
   integer, parameter, public          :: dp = kind(1.0d0)
   !! double precision
diff --git a/src/io.F90 b/src/io.F90
index 9c90f7adf..589799e98 100644
--- a/src/io.F90
+++ b/src/io.F90
@@ -425,13 +425,13 @@ function io_wallclocktime()
     ! Returns elapsed wall clock time in seconds since its first call  !
     !                                                                  !
     !===================================================================
-    use w90_constants, only: dp
+    use w90_constants, only: dp, i64
     implicit none
 
     real(kind=dp) :: io_wallclocktime
 
-    integer :: c0, c1
-    integer :: rate
+    integer(kind=i64) :: c0, c1
+    integer(kind=i64) :: rate
     logical :: first = .true.
     save first, rate, c0