diff --git a/test-tool/test_write10_residuals.c b/test-tool/test_write10_residuals.c
index 5250080..d8ab0fb 100644
--- a/test-tool/test_write10_residuals.c
+++ b/test-tool/test_write10_residuals.c
@@ -90,7 +90,10 @@ test_write10_residuals(void)
         iscsi_set_noautoreconnect(sd->iscsi_ctx, 1);
 
         for (i = 0; i < ARRAY_SIZE(write10_residuals); i++) {
-                write_residuals_test(&write10_residuals[i]);
+                bool command_is_implemented;
+
+                write_residuals_test(&write10_residuals[i],
+                                     &command_is_implemented);
 
                 if (!command_is_implemented) {
                         CU_PASS("WRITE10 is not implemented.");
diff --git a/test-tool/test_write12_residuals.c b/test-tool/test_write12_residuals.c
index ed23ff7..93856bd 100644
--- a/test-tool/test_write12_residuals.c
+++ b/test-tool/test_write12_residuals.c
@@ -90,7 +90,10 @@ test_write12_residuals(void)
         iscsi_set_noautoreconnect(sd->iscsi_ctx, 1);
 
         for (i = 0; i < ARRAY_SIZE(write12_residuals); i++) {
-                write_residuals_test(&write12_residuals[i]);
+                bool command_is_implemented;
+
+                write_residuals_test(&write12_residuals[i],
+                                     &command_is_implemented);
 
                 if (!command_is_implemented) {
                         CU_PASS("WRITE12 is not implemented.");
diff --git a/test-tool/test_write16_residuals.c b/test-tool/test_write16_residuals.c
index 78f6085..f7ebb58 100644
--- a/test-tool/test_write16_residuals.c
+++ b/test-tool/test_write16_residuals.c
@@ -90,7 +90,10 @@ test_write16_residuals(void)
         iscsi_set_noautoreconnect(sd->iscsi_ctx, 1);
 
         for (i = 0; i < ARRAY_SIZE(write16_residuals); i++) {
-                write_residuals_test(&write16_residuals[i]);
+                bool command_is_implemented;
+
+                write_residuals_test(&write16_residuals[i],
+                                     &command_is_implemented);
 
                 if (!command_is_implemented) {
                         CU_PASS("WRITE16 is not implemented.");
diff --git a/test-tool/test_write_residuals.c b/test-tool/test_write_residuals.c
index 99ac788..8865b23 100644
--- a/test-tool/test_write_residuals.c
+++ b/test-tool/test_write_residuals.c
@@ -29,10 +29,9 @@
 #include "iscsi-test-cu.h"
 #include "test_write_residuals.h"
 
-bool command_is_implemented = true;
-
 void
-write_residuals_test(const struct residuals_test_data *tdata)
+write_residuals_test(const struct residuals_test_data *tdata,
+                     bool *command_is_implemented)
 {
         struct iscsi_data data;
         struct scsi_task *task_ret;
@@ -49,6 +48,8 @@ write_residuals_test(const struct residuals_test_data *tdata)
 
         logging(LOG_VERBOSE, "\n%s", tdata->description);
 
+        *command_is_implemented = true;
+
         switch (tdata->cdb_size) {
         case 10:
                 scsi_opcode_write = SCSI_OPCODE_WRITE10;
@@ -122,7 +123,7 @@ write_residuals_test(const struct residuals_test_data *tdata)
             task->sense.key  == SCSI_SENSE_ILLEGAL_REQUEST &&
             task->sense.ascq == SCSI_SENSE_ASCQ_INVALID_OPERATION_CODE) {
                 logging(LOG_NORMAL, "[SKIPPED] WRITE%zu is not implemented.", tdata->cdb_size);
-                command_is_implemented = false;
+                *command_is_implemented = false;
                 scsi_free_scsi_task(task);
                 task = NULL;
                 return;
diff --git a/test-tool/test_write_residuals.h b/test-tool/test_write_residuals.h
index 4de3dd5..439b1a6 100644
--- a/test-tool/test_write_residuals.h
+++ b/test-tool/test_write_residuals.h
@@ -45,7 +45,7 @@ struct task_status {
   struct scsi_sense sense;
 };
 
-extern bool command_is_implemented;
-extern void write_residuals_test (const struct residuals_test_data *tdata);
+void write_residuals_test(const struct residuals_test_data *tdata,
+                          bool *command_is_implemented);
 
 #endif /* _ISCSI_TESTS_WRITE_RESIDUALS_H_ */