diff -urN a/src/arkode/fcmix/farknulllinsol.c b/src/arkode/fcmix/farknulllinsol.c
--- a/src/arkode/fcmix/farknulllinsol.c	2021-08-04 15:14:58.092488860 +0800
+++ b/src/arkode/fcmix/farknulllinsol.c	2021-08-04 15:06:12.679957136 +0800
@@ -26,8 +26,8 @@
 
 /* Define global matrix variables */
 
-SUNLinearSolver F2C_ARKODE_linsol;
-SUNLinearSolver F2C_ARKODE_mass_sol; 
+extern SUNLinearSolver F2C_ARKODE_linsol;
+extern SUNLinearSolver F2C_ARKODE_mass_sol; 
 
 /*=============================================================*/
 
diff -urN a/src/arkode/fcmix/farknullmatrix.c b/src/arkode/fcmix/farknullmatrix.c
--- a/src/arkode/fcmix/farknullmatrix.c	2021-08-04 15:15:14.396629485 +0800
+++ b/src/arkode/fcmix/farknullmatrix.c	2021-08-04 15:06:12.679957136 +0800
@@ -26,8 +26,8 @@
 
 /* Define global matrix variables */
 
-SUNMatrix F2C_ARKODE_matrix;
-SUNMatrix F2C_ARKODE_mass_matrix;
+extern SUNMatrix F2C_ARKODE_matrix;
+extern SUNMatrix F2C_ARKODE_mass_matrix;
 
 /*=============================================================*/
 
diff -urN a/src/sunlinsol/dense/fsunlinsol_dense.c b/src/sunlinsol/dense/fsunlinsol_dense.c
--- a/src/sunlinsol/dense/fsunlinsol_dense.c	2021-08-04 15:11:55.930917705 +0800
+++ b/src/sunlinsol/dense/fsunlinsol_dense.c	2021-08-04 15:13:55.679950547 +0800
@@ -25,11 +25,11 @@
 
 /* Define global linsol variables */
 
-SUNLinearSolver F2C_CVODE_linsol;
-SUNLinearSolver F2C_IDA_linsol;
-SUNLinearSolver F2C_KINSOL_linsol;
-SUNLinearSolver F2C_ARKODE_linsol;
-SUNLinearSolver F2C_ARKODE_mass_sol;
+extern SUNLinearSolver F2C_CVODE_linsol;
+extern SUNLinearSolver F2C_IDA_linsol;
+extern SUNLinearSolver F2C_KINSOL_linsol;
+extern SUNLinearSolver F2C_ARKODE_linsol;
+extern SUNLinearSolver F2C_ARKODE_mass_sol;
 
 /* Declarations of external global variables */
 
diff -urN a/src/sunlinsol/spgmr/fsunlinsol_spgmr.c b/src/sunlinsol/spgmr/fsunlinsol_spgmr.c
--- a/src/sunlinsol/spgmr/fsunlinsol_spgmr.c	2021-08-04 15:15:49.436931712 +0800
+++ b/src/sunlinsol/spgmr/fsunlinsol_spgmr.c	2021-08-04 15:06:12.679957136 +0800
@@ -25,11 +25,11 @@
 
 /* Define global linsol variables */
 
-SUNLinearSolver F2C_CVODE_linsol;
-SUNLinearSolver F2C_IDA_linsol;
-SUNLinearSolver F2C_KINSOL_linsol;
-SUNLinearSolver F2C_ARKODE_linsol;
-SUNLinearSolver F2C_ARKODE_mass_sol;
+extern SUNLinearSolver F2C_CVODE_linsol;
+extern SUNLinearSolver F2C_IDA_linsol;
+extern SUNLinearSolver F2C_KINSOL_linsol;
+extern SUNLinearSolver F2C_ARKODE_linsol;
+extern SUNLinearSolver F2C_ARKODE_mass_sol;
 
 /* Declarations of external global variables */
 
diff -urN a/src/sunmatrix/dense/fsunmatrix_dense.c b/src/sunmatrix/dense/fsunmatrix_dense.c
--- a/src/sunmatrix/dense/fsunmatrix_dense.c	2021-08-04 15:11:55.930917705 +0800
+++ b/src/sunmatrix/dense/fsunmatrix_dense.c	2021-08-04 15:13:10.683562450 +0800
@@ -25,11 +25,11 @@
 
 /* Define global matrix variables */
 
-SUNMatrix F2C_CVODE_matrix;
-SUNMatrix F2C_IDA_matrix;
-SUNMatrix F2C_KINSOL_matrix;
-SUNMatrix F2C_ARKODE_matrix;
-SUNMatrix F2C_ARKODE_mass_matrix;
+extern SUNMatrix F2C_CVODE_matrix;
+extern SUNMatrix F2C_IDA_matrix;
+extern SUNMatrix F2C_KINSOL_matrix;
+extern SUNMatrix F2C_ARKODE_matrix;
+extern SUNMatrix F2C_ARKODE_mass_matrix;
 
 /* Fortran callable interfaces */
 
diff -urN a/src/cvode/fcmix/fcvnulllinsol.c b/src/cvode/fcmix/fcvnulllinsol.c
--- a/src/cvode/fcmix/fcvnulllinsol.c	2021-08-04 16:13:56.423007237 +0800
+++ b/src/cvode/fcmix/fcvnulllinsol.c	2021-08-04 16:16:46.760476411 +0800
@@ -26,7 +26,7 @@
 
 /* Define global linear solver variable */
 
-SUNLinearSolver F2C_CVODE_linsol;
+extern SUNLinearSolver F2C_CVODE_linsol;
 
 /*=============================================================*/
 
diff -urN a/src/cvode/fcmix/fcvnullmatrix.c b/src/cvode/fcmix/fcvnullmatrix.c
--- a/src/cvode/fcmix/fcvnullmatrix.c	2021-08-04 16:13:56.423007237 +0800
+++ b/src/cvode/fcmix/fcvnullmatrix.c	2021-08-04 16:17:07.408654503 +0800
@@ -26,7 +26,7 @@
 
 /* Define global matrix variable */
 
-SUNMatrix F2C_CVODE_matrix;
+extern SUNMatrix F2C_CVODE_matrix;
 
 /*=============================================================*/
 
diff -urN a/src/cvode/fcmix/fcvnullnonlinsol.c b/src/cvode/fcmix/fcvnullnonlinsol.c
--- a/src/cvode/fcmix/fcvnullnonlinsol.c	2021-08-04 16:13:56.423007237 +0800
+++ b/src/cvode/fcmix/fcvnullnonlinsol.c	2021-08-04 16:17:31.512862405 +0800
@@ -26,7 +26,7 @@
 
 /* Define global linear solver variable */
 
-SUNNonlinearSolver F2C_CVODE_nonlinsol;
+extern SUNNonlinearSolver F2C_CVODE_nonlinsol;
 
 /*=============================================================*/
 
diff -urN a/src/sunmatrix/sparse/fsunmatrix_sparse.c b/src/sunmatrix/sparse/fsunmatrix_sparse.c
--- a/src/sunmatrix/sparse/fsunmatrix_sparse.c	2021-08-04 16:27:46.222164321 +0800
+++ b/src/sunmatrix/sparse/fsunmatrix_sparse.c	2021-08-04 16:28:54.458752870 +0800
@@ -26,7 +26,7 @@
 /* Define global matrix variables */
 
 SUNMatrix F2C_CVODE_matrix;
-SUNMatrix F2C_IDA_matrix;
+extern SUNMatrix F2C_IDA_matrix;
 SUNMatrix F2C_KINSOL_matrix;
 SUNMatrix F2C_ARKODE_matrix;
 SUNMatrix F2C_ARKODE_mass_matrix;
diff -urN a/src/kinsol/fcmix/fkinnullmatrix.c b/src/kinsol/fcmix/fkinnullmatrix.c
--- a/src/kinsol/fcmix/fkinnullmatrix.c	2021-08-04 16:33:54.485340623 +0800
+++ b/src/kinsol/fcmix/fkinnullmatrix.c	2021-08-04 16:34:24.573600132 +0800
@@ -26,7 +26,7 @@
 
 /* Define global matrix variable */
 
-SUNMatrix F2C_KINSOL_matrix;
+extern SUNMatrix F2C_KINSOL_matrix;
 
 /*=============================================================*/
 
diff -urN a/src/kinsol/fcmix/fkinnulllinsol.c b/src/kinsol/fcmix/fkinnulllinsol.c
--- a/src/kinsol/fcmix/fkinnulllinsol.c	2021-08-04 16:40:38.028821213 +0800
+++ b/src/kinsol/fcmix/fkinnulllinsol.c	2021-08-04 16:41:02.225029907 +0800
@@ -26,7 +26,7 @@
 
 /* Define global linear solver variable */
 
-SUNLinearSolver F2C_KINSOL_linsol;
+extern SUNLinearSolver F2C_KINSOL_linsol;
 
 /*=============================================================*/
 
