diff --git a/include/matador/query/attribute_string_writer.hpp b/include/matador/query/attribute_string_writer.hpp
index 53cb3d4..ebca79f 100644
--- a/include/matador/query/attribute_string_writer.hpp
+++ b/include/matador/query/attribute_string_writer.hpp
@@ -3,17 +3,13 @@
 
 #include "matador/utils/attribute_writer.hpp"
 
-#include <optional>
+#include "matador/sql/interface/connection_impl.hpp"
 
-namespace matador::sql {
-class dialect;
-class connection_impl;
-}
+#include <optional>
 
 namespace matador::query {
 
-class attribute_string_writer final : public utils::attribute_writer
-{
+class attribute_string_writer final : public utils::attribute_writer {
 public:
   attribute_string_writer(const sql::dialect &d, std::optional<std::reference_wrapper<const sql::connection_impl>> conn);
 
diff --git a/include/matador/query/insert_query_builder.hpp b/include/matador/query/insert_query_builder.hpp
index 00da271..0f8acd9 100644
--- a/include/matador/query/insert_query_builder.hpp
+++ b/include/matador/query/insert_query_builder.hpp
@@ -1,8 +1,6 @@
 #ifndef MATADOR_INSERT_QUERY_BUILDER_HPP
 #define MATADOR_INSERT_QUERY_BUILDER_HPP
 
-#include <utility>
-
 #include "matador/object/collection.hpp"
 #include "matador/object/object_ptr.hpp"
 
diff --git a/include/matador/query/query_builder.hpp b/include/matador/query/query_builder.hpp
index 8957be5..18898fa 100644
--- a/include/matador/query/query_builder.hpp
+++ b/include/matador/query/query_builder.hpp
@@ -5,6 +5,7 @@
 #include "matador/query/query_data.hpp"
 
 #include "matador/sql/query_context.hpp"
+#include "matador/sql/interface/connection_impl.hpp"
 
 #include "matador/utils/placeholder.hpp"
 
@@ -12,7 +13,6 @@
 #include <optional>
 
 namespace matador::sql {
-class connection_impl;
 class dialect;
 }
 
@@ -33,7 +33,6 @@ public:
                            const sql::dialect &d,
                            std::optional<std::reference_wrapper<const sql::connection_impl>> conn);
 
-protected:
   void visit(internal::query_alter_part& part) override;
   void visit(internal::query_alter_table_part& part) override;
   void visit(internal::query_add_key_constraint_part& part) override;
diff --git a/include/matador/query/query_utils.hpp b/include/matador/query/query_utils.hpp
index a3d71d4..2c4c982 100644
--- a/include/matador/query/query_utils.hpp
+++ b/include/matador/query/query_utils.hpp
@@ -1,8 +1,7 @@
 #ifndef MATADOR_QUERY_UTILS_HPP
 #define MATADOR_QUERY_UTILS_HPP
 
-#include "table.hpp"
-#include "matador/sql/dialect.hpp"
+#include "matador/utils/value.hpp"
 
 #include <string>
 
@@ -11,6 +10,7 @@ class dialect;
 struct query_context;
 }
 namespace matador::query {
+class table;
 class table_column;
 
 void prepare_column(sql::query_context& ctx, const sql::dialect& d, const table_column& col);
diff --git a/include/matador/sql/interface/connection_impl.hpp b/include/matador/sql/interface/connection_impl.hpp
index 57ad095..72f137e 100644
--- a/include/matador/sql/interface/connection_impl.hpp
+++ b/include/matador/sql/interface/connection_impl.hpp
@@ -5,6 +5,7 @@
 
 #include "matador/object/attribute.hpp"
 
+#include "matador/sql/dialect.hpp"
 #include "matador/sql/connection_info.hpp"
 #include "matador/sql/execute_result.hpp"
 
@@ -17,13 +18,11 @@ using blob_type_t = std::vector<unsigned char>;
 }
 
 namespace matador::sql {
-
 struct query_context;
 class query_result_impl;
 class statement_impl;
 
-class connection_impl
-{
+class connection_impl {
 public:
   virtual ~connection_impl() = default;
 
diff --git a/source/orm/query/attribute_string_writer.cpp b/source/orm/query/attribute_string_writer.cpp
index 9ce0af6..fa90210 100644
--- a/source/orm/query/attribute_string_writer.cpp
+++ b/source/orm/query/attribute_string_writer.cpp
@@ -2,7 +2,6 @@
 
 #include "matador/query/query_utils.hpp"
 
-#include "matador/sql/interface/connection_impl.hpp"
 #include "matador/sql/dialect.hpp"
 
 #include <matador/utils/convert.hpp>
diff --git a/source/orm/query/query_builder.cpp b/source/orm/query/query_builder.cpp
index 8ae12c0..3754400 100644
--- a/source/orm/query/query_builder.cpp
+++ b/source/orm/query/query_builder.cpp
@@ -12,8 +12,6 @@
 #include "matador/query/internal/string_builder_utils.hpp"
 #include "matador/query/internal/query_parts.hpp"
 
-#include "matador/sql/interface/connection_impl.hpp"
-
 #include "matador/sql/query_context.hpp"
 #include "matador/sql/dialect.hpp"