diff --git a/src/LAPACK_interface.f90 b/src/LAPACK_interface.f90
index e11f74875..43ddb5771 100644
--- a/src/LAPACK_interface.f90
+++ b/src/LAPACK_interface.f90
@@ -8,6 +8,8 @@ module LAPACK_interface
 
     pure subroutine dgeev(jobvl,jobvr,n,a,lda,wr,wi,vl,ldvl,vr,ldvr,work,lwork,info)
       use prec
+      implicit none
+
       character,   intent(in)                             :: jobvl,jobvr
       integer,     intent(in)                             :: n,lda,ldvl,ldvr,lwork
       real(pReal), intent(inout), dimension(lda,n)        :: a
@@ -20,6 +22,8 @@ module LAPACK_interface
 
     pure subroutine dgesv(n,nrhs,a,lda,ipiv,b,ldb,info)
       use prec
+      implicit none
+
       integer,     intent(in)                             :: n,nrhs,lda,ldb
       real(pReal), intent(inout), dimension(lda,n)        :: a
       integer,     intent(out),   dimension(n)            :: ipiv
@@ -29,6 +33,8 @@ module LAPACK_interface
 
     pure subroutine dgetrf(m,n,a,lda,ipiv,info)
       use prec
+      implicit none
+
       integer,     intent(in)                             :: m,n,lda
       real(pReal), intent(inout), dimension(lda,n)        :: a
       integer,     intent(out),   dimension(min(m,n))     :: ipiv
@@ -37,6 +43,8 @@ module LAPACK_interface
 
     pure subroutine dgetri(n,a,lda,ipiv,work,lwork,info)
       use prec
+      implicit none
+
       integer,     intent(in)                             :: n,lda,lwork
       real(pReal), intent(inout), dimension(lda,n)        :: a
       integer,     intent(in),    dimension(n)            :: ipiv
@@ -46,6 +54,8 @@ module LAPACK_interface
 
     pure subroutine dsyev(jobz,uplo,n,a,lda,w,work,lwork,info)
       use prec
+      implicit none
+
       character,   intent(in)                             :: jobz,uplo
       integer,     intent(in)                             :: n,lda,lwork
       real(pReal), intent(inout), dimension(lda,n)        :: a
diff --git a/src/YAML_parse.f90 b/src/YAML_parse.f90
index bfce06bc9..a887476a9 100644
--- a/src/YAML_parse.f90
+++ b/src/YAML_parse.f90
@@ -24,6 +24,7 @@ module YAML_parse
 
     subroutine to_flow_C(flow,length_flow,mixed) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_INT, C_CHAR, C_PTR
+      implicit none
 
       type(C_PTR), intent(out) :: flow
       integer(C_INT), intent(out) :: length_flow
diff --git a/src/grid/zlib.f90 b/src/grid/zlib.f90
index 21428255c..10a62a55b 100644
--- a/src/grid/zlib.f90
+++ b/src/grid/zlib.f90
@@ -13,15 +13,14 @@ module zlib
 
   interface
 
-  subroutine inflate_C(s_deflated,s_inflated,deflated,inflated) bind(C)
-    use, intrinsic :: ISO_C_Binding, only: &
-      C_SIGNED_CHAR, C_INT64_T
+    subroutine inflate_C(s_deflated,s_inflated,deflated,inflated) bind(C)
+      use, intrinsic :: ISO_C_Binding, only: C_SIGNED_CHAR, C_INT64_T
+      implicit none
 
-    integer(C_INT64_T),                            intent(in)  :: s_deflated,s_inflated
-    integer(C_SIGNED_CHAR), dimension(s_deflated), intent(in)  :: deflated
-    integer(C_SIGNED_CHAR), dimension(s_inflated), intent(out) :: inflated
-
-  end subroutine inflate_C
+      integer(C_INT64_T),                            intent(in)  :: s_deflated,s_inflated
+      integer(C_SIGNED_CHAR), dimension(s_deflated), intent(in)  :: deflated
+      integer(C_SIGNED_CHAR), dimension(s_inflated), intent(out) :: inflated
+    end subroutine inflate_C
 
   end interface
 
@@ -37,6 +36,7 @@ function zlib_inflate(deflated,size_inflated)
 
   integer(C_SIGNED_CHAR), dimension(size_inflated) :: zlib_inflate
 
+
   call inflate_C(size(deflated,kind=C_INT64_T),int(size_inflated,C_INT64_T),deflated,zlib_inflate)
 
 end function zlib_inflate
diff --git a/src/system_routines.f90 b/src/system_routines.f90
index 2af1e12a9..209013be4 100644
--- a/src/system_routines.f90
+++ b/src/system_routines.f90
@@ -24,8 +24,10 @@ module system_routines
 
   interface
 
+
     function setCWD_C(cwd) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_INT, C_CHAR
+      implicit none
 
       integer(C_INT) :: setCWD_C
       character(kind=C_CHAR), dimension(*), intent(in) :: cwd
@@ -34,6 +36,7 @@ module system_routines
     subroutine getCWD_C(cwd, stat) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_INT, C_CHAR
       use prec
+      implicit none
 
       character(kind=C_CHAR), dimension(pPathLen+1), intent(out) :: cwd                             ! NULL-terminated array
       integer(C_INT),                                intent(out) :: stat
@@ -42,6 +45,7 @@ module system_routines
     subroutine getHostName_C(hostname, stat) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_INT, C_CHAR
       use prec
+      implicit none
 
       character(kind=C_CHAR), dimension(pStringLen+1), intent(out) :: hostname                        ! NULL-terminated array
       integer(C_INT),                                  intent(out) :: stat
@@ -50,6 +54,7 @@ module system_routines
     subroutine getUserName_C(username, stat) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_INT, C_CHAR
       use prec
+      implicit none
 
       character(kind=C_CHAR), dimension(pStringLen+1), intent(out) :: username                        ! NULL-terminated array
       integer(C_INT),                                  intent(out) :: stat
@@ -57,27 +62,31 @@ module system_routines
 
     subroutine signalint_C(handler) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_FUNPTR
+      implicit none
 
       type(C_FUNPTR), intent(in), value :: handler
     end subroutine signalint_C
 
     subroutine signalusr1_C(handler) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_FUNPTR
+      implicit none
 
       type(C_FUNPTR), intent(in), value :: handler
     end subroutine signalusr1_C
 
     subroutine signalusr2_C(handler) bind(C)
       use, intrinsic :: ISO_C_Binding, only: C_FUNPTR
+      implicit none
 
       type(C_FUNPTR), intent(in), value :: handler
     end subroutine signalusr2_C
 
     subroutine free_C(ptr) bind(C,name='free')
-      import c_ptr
-      type(c_ptr), value :: ptr
-    end subroutine free_C
+      use, intrinsic :: ISO_C_Binding, only: C_PTR
+      implicit none
 
+      type(C_PTR), value :: ptr
+    end subroutine free_C
 
   end interface