diff --git a/app/vminsert/graphite/parser.go b/app/vminsert/graphite/parser.go
index 77bad97c52..a33ac2fa4e 100644
--- a/app/vminsert/graphite/parser.go
+++ b/app/vminsert/graphite/parser.go
@@ -114,6 +114,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag) ([]Row, []Tag, error) {
 			var err error
 			tagsPool, err = r.unmarshal(s, tagsPool)
 			if err != nil {
+				err = fmt.Errorf("cannot unmarshal Graphite line %q: %s", s, err)
 				return dst, tagsPool, err
 			}
 			return dst, tagsPool, nil
@@ -121,6 +122,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag) ([]Row, []Tag, error) {
 		var err error
 		tagsPool, err = r.unmarshal(s[:n], tagsPool)
 		if err != nil {
+			err = fmt.Errorf("cannot unmarshal Graphite line %q: %s", s[:n], err)
 			return dst, tagsPool, err
 		}
 		s = s[n+1:]
diff --git a/app/vminsert/influx/parser.go b/app/vminsert/influx/parser.go
index 890bf5b81e..a8568726cb 100644
--- a/app/vminsert/influx/parser.go
+++ b/app/vminsert/influx/parser.go
@@ -196,6 +196,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag, fieldsPool []Field) ([]R
 			var err error
 			tagsPool, fieldsPool, err = r.unmarshal(s, tagsPool, fieldsPool)
 			if err != nil {
+				err = fmt.Errorf("cannot unmarshal Influx line %q: %s", s, err)
 				return dst, tagsPool, fieldsPool, err
 			}
 			return dst, tagsPool, fieldsPool, nil
@@ -203,6 +204,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag, fieldsPool []Field) ([]R
 		var err error
 		tagsPool, fieldsPool, err = r.unmarshal(s[:n], tagsPool, fieldsPool)
 		if err != nil {
+			err = fmt.Errorf("cannot unmarshal Influx line %q: %s", s[:n], err)
 			return dst, tagsPool, fieldsPool, err
 		}
 		s = s[n+1:]
diff --git a/app/vminsert/opentsdb/parser.go b/app/vminsert/opentsdb/parser.go
index 31d2b172df..e68b908174 100644
--- a/app/vminsert/opentsdb/parser.go
+++ b/app/vminsert/opentsdb/parser.go
@@ -111,6 +111,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag) ([]Row, []Tag, error) {
 			var err error
 			tagsPool, err = r.unmarshal(s, tagsPool)
 			if err != nil {
+				err = fmt.Errorf("cannot unmarshal OpenTSDB line %q: %s", s, err)
 				return dst, tagsPool, err
 			}
 			return dst, tagsPool, nil
@@ -118,6 +119,7 @@ func unmarshalRows(dst []Row, s string, tagsPool []Tag) ([]Row, []Tag, error) {
 		var err error
 		tagsPool, err = r.unmarshal(s[:n], tagsPool)
 		if err != nil {
+			err = fmt.Errorf("cannot unmarshal OpenTSDB line %q: %s", s[:n], err)
 			return dst, tagsPool, err
 		}
 		s = s[n+1:]