diff --git a/src/sql/kernel/qsqlfield.h b/src/sql/kernel/qsqlfield.h
index 58dce8b271f..f5cda7ea64f 100644
--- a/src/sql/kernel/qsqlfield.h
+++ b/src/sql/kernel/qsqlfield.h
@@ -57,8 +57,8 @@ class Q_SQL_EXPORT QSqlField
 public:
     enum RequiredStatus { Unknown = -1, Optional = 0, Required = 1 };
 
-    QSqlField(const QString& fieldName = QString(),
-              QVariant::Type type = QVariant::Invalid);
+    explicit QSqlField(const QString& fieldName = QString(),
+                       QVariant::Type type = QVariant::Invalid);
 
     QSqlField(const QSqlField& other);
     QSqlField& operator=(const QSqlField& other);
diff --git a/src/sql/kernel/qsqlindex.h b/src/sql/kernel/qsqlindex.h
index e3e55b690eb..0af63ab67cf 100644
--- a/src/sql/kernel/qsqlindex.h
+++ b/src/sql/kernel/qsqlindex.h
@@ -54,7 +54,7 @@ QT_BEGIN_NAMESPACE
 class Q_SQL_EXPORT QSqlIndex : public QSqlRecord
 {
 public:
-    QSqlIndex(const QString &cursorName = QString(), const QString &name = QString());
+    explicit QSqlIndex(const QString &cursorName = QString(), const QString &name = QString());
     QSqlIndex(const QSqlIndex &other);
     ~QSqlIndex();
     QSqlIndex &operator=(const QSqlIndex &other);
diff --git a/src/sql/kernel/qsqlquery.h b/src/sql/kernel/qsqlquery.h
index 930bb25abf4..19df1d52bb3 100644
--- a/src/sql/kernel/qsqlquery.h
+++ b/src/sql/kernel/qsqlquery.h
@@ -62,8 +62,8 @@ class QSqlQueryPrivate;
 class Q_SQL_EXPORT QSqlQuery
 {
 public:
-    QSqlQuery(QSqlResult *r);
-    QSqlQuery(const QString& query = QString(), QSqlDatabase db = QSqlDatabase());
+    explicit QSqlQuery(QSqlResult *r);
+    explicit QSqlQuery(const QString& query = QString(), QSqlDatabase db = QSqlDatabase());
     explicit QSqlQuery(QSqlDatabase db);
     QSqlQuery(const QSqlQuery& other);
     QSqlQuery& operator=(const QSqlQuery& other);