diff --git a/src/box/applier.cc b/src/box/applier.cc
index 8666a3a98418d33eebb35c7546ac03603360d956..47a26c36629a5990a512a17ba5a77720da16eb97 100644
--- a/src/box/applier.cc
+++ b/src/box/applier.cc
@@ -843,7 +843,7 @@ applier_on_rollback(struct trigger *trigger, void *event)
 	struct applier *applier = (struct applier *)trigger->data;
 	/* Setup a shared error. */
 	if (!diag_is_empty(&replicaset.applier.diag)) {
-		diag_add_error(&applier->diag,
+		diag_set_error(&applier->diag,
 			       diag_last_error(&replicaset.applier.diag));
 	}
 	/* Stop the applier fiber. */
diff --git a/src/box/error.cc b/src/box/error.cc
index 47dce3305a3db65585f81405fdaa256df99b0df7..7dfe1b3eed3669213f327a753d72fa813396db83 100644
--- a/src/box/error.cc
+++ b/src/box/error.cc
@@ -82,7 +82,7 @@ box_error_set(const char *file, unsigned line, uint32_t code,
 		error_vformat_msg(e, fmt, ap);
 		va_end(ap);
 	}
-	diag_add_error(&fiber()->diag, e);
+	diag_set_error(&fiber()->diag, e);
 	return -1;
 }
 
diff --git a/src/box/relay.cc b/src/box/relay.cc
index 95245a3cfa6cf2c340e08d291f0756f4ae10ec61..c634348a48f1a0097ad95047904ce9747bbd47df 100644
--- a/src/box/relay.cc
+++ b/src/box/relay.cc
@@ -479,7 +479,7 @@ relay_set_error(struct relay *relay, struct error *e)
 {
 	/* Don't override existing error. */
 	if (diag_is_empty(&relay->diag))
-		diag_add_error(&relay->diag, e);
+		diag_set_error(&relay->diag, e);
 }
 
 static void
@@ -658,7 +658,7 @@ relay_subscribe_f(va_list ap)
 	 * Don't clear the error for status reporting.
 	 */
 	assert(!diag_is_empty(&relay->diag));
-	diag_add_error(diag_get(), diag_last_error(&relay->diag));
+	diag_set_error(diag_get(), diag_last_error(&relay->diag));
 	diag_log();
 	say_crit("exiting the relay loop");
 
diff --git a/src/box/vy_scheduler.c b/src/box/vy_scheduler.c
index acc909d09a0bd214fedeba9f819c9a6c4e3c7843..bf4c3fe58eda8088f139cd2c7e82e57325aaaf40 100644
--- a/src/box/vy_scheduler.c
+++ b/src/box/vy_scheduler.c
@@ -619,7 +619,7 @@ vy_scheduler_dump(struct vy_scheduler *scheduler)
 		if (scheduler->is_throttled) {
 			/* Dump error occurred. */
 			struct error *e = diag_last_error(&scheduler->diag);
-			diag_add_error(diag_get(), e);
+			diag_set_error(diag_get(), e);
 			return -1;
 		}
 		fiber_cond_wait(&scheduler->dump_cond);
@@ -693,7 +693,7 @@ vy_scheduler_begin_checkpoint(struct vy_scheduler *scheduler)
 	 */
 	if (scheduler->is_throttled) {
 		struct error *e = diag_last_error(&scheduler->diag);
-		diag_add_error(diag_get(), e);
+		diag_set_error(diag_get(), e);
 		say_error("cannot checkpoint vinyl, "
 			  "scheduler is throttled with: %s", e->errmsg);
 		return -1;
@@ -729,7 +729,7 @@ vy_scheduler_wait_checkpoint(struct vy_scheduler *scheduler)
 		if (scheduler->is_throttled) {
 			/* A dump error occurred, abort checkpoint. */
 			struct error *e = diag_last_error(&scheduler->diag);
-			diag_add_error(diag_get(), e);
+			diag_set_error(diag_get(), e);
 			say_error("vinyl checkpoint failed: %s", e->errmsg);
 			return -1;
 		}
diff --git a/src/lib/core/diag.h b/src/lib/core/diag.h
index f763957c201f5d3ce7fd809d87078a5e5297c293..7e1e1a174d1b61b8dae1de897a139a781a1d252c 100644
--- a/src/lib/core/diag.h
+++ b/src/lib/core/diag.h
@@ -168,12 +168,12 @@ diag_clear(struct diag *diag)
 }
 
 /**
- * Add a new error to the diagnostics area
+ * Set a new error to the diagnostics area, replacing existent.
  * \param diag diagnostics area
  * \param e error to add
  */
 static inline void
-diag_add_error(struct diag *diag, struct error *e)
+diag_set_error(struct diag *diag, struct error *e)
 {
 	assert(e != NULL);
 	error_ref(e);
@@ -275,7 +275,7 @@ BuildSocketError(const char *file, unsigned line, const char *socketname,
 	say_debug("%s at %s:%i", #class, __FILE__, __LINE__);		\
 	struct error *e;						\
 	e = Build##class(__FILE__, __LINE__, ##__VA_ARGS__);		\
-	diag_add_error(diag_get(), e);					\
+	diag_set_error(diag_get(), e);					\
 	/* Restore the errno which might have been reset.  */           \
 	errno = save_errno;                                             \
 } while (0)
diff --git a/src/lib/core/exception.cc b/src/lib/core/exception.cc
index 76dcea5536cdc7541170a385390b3b865f7c603f..0ab10c4bdd59211a534330d180d19f8c3a8b90a2 100644
--- a/src/lib/core/exception.cc
+++ b/src/lib/core/exception.cc
@@ -99,7 +99,7 @@ Exception::operator new(size_t size)
 	void *buf = malloc(size);
 	if (buf != NULL)
 		return buf;
-	diag_add_error(diag_get(), &out_of_memory);
+	diag_set_error(diag_get(), &out_of_memory);
 	throw &out_of_memory;
 }
 
diff --git a/src/lib/core/exception.h b/src/lib/core/exception.h
index d6154eb328c583d5038fdfd5ed45087f1368a67a..1947b4f005fccd24a3169344f079d7d9e77e8550 100644
--- a/src/lib/core/exception.h
+++ b/src/lib/core/exception.h
@@ -177,7 +177,7 @@ exception_init();
 #define tnt_error(class, ...) ({					\
 	say_debug("%s at %s:%i", #class, __FILE__, __LINE__);		\
 	class *e = new class(__FILE__, __LINE__, ##__VA_ARGS__);	\
-	diag_add_error(diag_get(), e);					\
+	diag_set_error(diag_get(), e);					\
 	e;								\
 })
 
diff --git a/src/lua/utils.c b/src/lua/utils.c
index de14c778c6dad685d4f2105de646b22a5eb72e11..54d18ac89334f98306d7efa1fcf21b57bd252087 100644
--- a/src/lua/utils.c
+++ b/src/lua/utils.c
@@ -1022,7 +1022,7 @@ luaT_toerror(lua_State *L)
 	struct error *e = luaL_iserror(L, -1);
 	if (e != NULL) {
 		/* Re-throw original error */
-		diag_add_error(&fiber()->diag, e);
+		diag_set_error(&fiber()->diag, e);
 	} else {
 		/* Convert Lua error to a Tarantool exception. */
 		diag_set(LuajitError, luaT_tolstring(L, -1, NULL));