diff --git a/src/LAPACK_interface.f90 b/src/LAPACK_interface.f90
index 91d2451a4..e11f74875 100644
--- a/src/LAPACK_interface.f90
+++ b/src/LAPACK_interface.f90
@@ -6,7 +6,7 @@
 module LAPACK_interface
   interface
 
-    subroutine dgeev(jobvl,jobvr,n,a,lda,wr,wi,vl,ldvl,vr,ldvr,work,lwork,info)
+    pure subroutine dgeev(jobvl,jobvr,n,a,lda,wr,wi,vl,ldvl,vr,ldvr,work,lwork,info)
       use prec
       character,   intent(in)                             :: jobvl,jobvr
       integer,     intent(in)                             :: n,lda,ldvl,ldvr,lwork
@@ -18,7 +18,7 @@ module LAPACK_interface
       integer,     intent(out)                            :: info
     end subroutine dgeev
 
-    subroutine dgesv(n,nrhs,a,lda,ipiv,b,ldb,info)
+    pure subroutine dgesv(n,nrhs,a,lda,ipiv,b,ldb,info)
       use prec
       integer,     intent(in)                             :: n,nrhs,lda,ldb
       real(pReal), intent(inout), dimension(lda,n)        :: a
@@ -27,7 +27,7 @@ module LAPACK_interface
       integer,     intent(out)                            :: info
     end subroutine dgesv
 
-    subroutine dgetrf(m,n,a,lda,ipiv,info)
+    pure subroutine dgetrf(m,n,a,lda,ipiv,info)
       use prec
       integer,     intent(in)                             :: m,n,lda
       real(pReal), intent(inout), dimension(lda,n)        :: a
@@ -35,7 +35,7 @@ module LAPACK_interface
       integer,     intent(out)                            :: info
     end subroutine dgetrf
 
-    subroutine dgetri(n,a,lda,ipiv,work,lwork,info)
+    pure subroutine dgetri(n,a,lda,ipiv,work,lwork,info)
       use prec
       integer,     intent(in)                             :: n,lda,lwork
       real(pReal), intent(inout), dimension(lda,n)        :: a
@@ -44,7 +44,7 @@ module LAPACK_interface
       integer,     intent(out)                            :: info
     end subroutine dgetri
 
-    subroutine dsyev(jobz,uplo,n,a,lda,w,work,lwork,info)
+    pure subroutine dsyev(jobz,uplo,n,a,lda,w,work,lwork,info)
       use prec
       character,   intent(in)                             :: jobz,uplo
       integer,     intent(in)                             :: n,lda,lwork