diff --git a/src/sparse_sys.c b/src/sparse_sys.c
index 44790448..77637ee6 100644
--- a/src/sparse_sys.c
+++ b/src/sparse_sys.c
@@ -203,41 +203,60 @@ void
 csrmatrix_write(const struct CSRMatrix *A, const char *fn)
 /* ---------------------------------------------------------------------- */
 {
-    size_t  i, j;
-    FILE   *fp;
+    FILE *fp;
 
     fp = fopen(fn, "wt");
 
     if (fp != NULL) {
-        for (i = j = 0; i < A->m; i++) {
-            for (; j < (size_t) (A->ia[i + 1]); j++) {
-                fprintf(fp, "%lu %lu %26.18e\n",
-                        (unsigned long) (i + 1),
-                        (unsigned long) (A->ja[j] + 1),
-                        A->sa[j]);
-            }
-        }
+        csrmatrix_write_stream(A, fp);
     }
 
     fclose(fp);
 }
 
 
+/* ---------------------------------------------------------------------- */
+void
+csrmatrix_write_stream(const struct CSRMatrix *A, FILE *fp)
+/* ---------------------------------------------------------------------- */
+{
+    size_t  i, j;
+    for (i = j = 0; i < A->m; i++) {
+        for (; j < (size_t) (A->ia[i + 1]); j++) {
+            fprintf(fp, "%lu %lu %26.18e\n",
+                    (unsigned long) (i + 1),
+                    (unsigned long) (A->ja[j] + 1),
+                    A->sa[j]);
+        }
+    }
+}
+
+
 /* ---------------------------------------------------------------------- */
 void
 vector_write(size_t n, const double *v, const char *fn)
 /* ---------------------------------------------------------------------- */
 {
-    size_t  i;
-    FILE   *fp;
+    FILE *fp;
 
     fp = fopen(fn, "wt");
 
     if (fp != NULL) {
-        for (i = 0; i < n; i++) {
-            fprintf(fp, "%26.18e\n", v[i]);
-        }
+        vector_write_stream(n, v, fp);
     }
     
     fclose(fp);
 }
+
+
+/* ---------------------------------------------------------------------- */
+void
+vector_write_stream(size_t n, const double *v, FILE *fp)
+/* ---------------------------------------------------------------------- */
+{
+    size_t i;
+
+    for (i = 0; i < n; i++) {
+        fprintf(fp, "%26.18e\n", v[i]);
+    }
+}
diff --git a/src/sparse_sys.h b/src/sparse_sys.h
index e48dcf24..d1788ed5 100644
--- a/src/sparse_sys.h
+++ b/src/sparse_sys.h
@@ -21,6 +21,7 @@
 #define OPM_SPARSE_SYS_HEADER_INCLUDED
 
 #include <stddef.h>
+#include <stdio.h>
 
 #ifdef __cplusplus
 extern "C" {
@@ -70,9 +71,15 @@ vector_zero(size_t n, double *v);
 void
 csrmatrix_write(const struct CSRMatrix *A, const char *fn);
 
+void
+csrmatrix_write_stream(const struct CSRMatrix *A, FILE *fp);
+
 void
 vector_write(size_t n, const double *v, const char *fn);
 
+void
+vector_write_stream(size_t n, const double *v, FILE *fp);
+
 #ifdef __cplusplus
 }
 #endif