diff --git a/src/core/json/include/sourcemeta/core/json.h b/src/core/json/include/sourcemeta/core/json.h
index 0603ca35c..a3c835e32 100644
--- a/src/core/json/include/sourcemeta/core/json.h
+++ b/src/core/json/include/sourcemeta/core/json.h
@@ -5,7 +5,6 @@
 #include <sourcemeta/core/json_export.h>
 #endif
 
-#include <sourcemeta/core/json_hash.h>
 #include <sourcemeta/core/json_value.h>
 
 #include <cstdint>    // std::uint64_t
diff --git a/src/core/json/include/sourcemeta/core/json_error.h b/src/core/json/include/sourcemeta/core/json_error.h
index 0fe1e3c6f..d8a9dbc5a 100644
--- a/src/core/json/include/sourcemeta/core/json_error.h
+++ b/src/core/json/include/sourcemeta/core/json_error.h
@@ -8,6 +8,8 @@
 #include <cstdint>    // std::uint64_t
 #include <exception>  // std::exception
 #include <filesystem> // std::filesystem::path
+#include <string>     // std::string
+#include <utility>    // std::move
 
 namespace sourcemeta::core {
 
diff --git a/src/core/json/include/sourcemeta/core/json_object.h b/src/core/json/include/sourcemeta/core/json_object.h
index 7885fbdd0..5500a5344 100644
--- a/src/core/json/include/sourcemeta/core/json_object.h
+++ b/src/core/json/include/sourcemeta/core/json_object.h
@@ -3,7 +3,7 @@
 
 #include <algorithm>        // std::swap
 #include <cassert>          // assert
-#include <functional>       // std::equal_to, std::less
+#include <cstddef>          // std::size_t
 #include <initializer_list> // std::initializer_list
 #include <iterator>         // std::advance
 #include <utility>          // std::pair, std::move
diff --git a/src/core/json/include/sourcemeta/core/json_value.h b/src/core/json/include/sourcemeta/core/json_value.h
index 96b36dbc5..f3f673d99 100644
--- a/src/core/json/include/sourcemeta/core/json_value.h
+++ b/src/core/json/include/sourcemeta/core/json_value.h
@@ -11,11 +11,11 @@
 
 #include <algorithm>        // std::any_of
 #include <cassert>          // assert
+#include <cstddef>          // std::size_t
 #include <cstdint>          // std::int64_t, std::uint8_t
 #include <functional>       // std::less, std::reference_wrapper, std::function
 #include <initializer_list> // std::initializer_list
 #include <memory>           // std::allocator
-#include <optional>         // std::optional
 #include <set>              // std::set
 #include <sstream>          // std::basic_istringstream
 #include <string>           // std::basic_string, std::char_traits
diff --git a/src/core/json/json.cc b/src/core/json/json.cc
index 3479296ac..6e420882b 100644
--- a/src/core/json/json.cc
+++ b/src/core/json/json.cc
@@ -2,9 +2,15 @@
 #include "stringify.h"
 
 #include <sourcemeta/core/json.h>
+#include <sourcemeta/core/json_error.h>
+#include <sourcemeta/core/json_value.h>
 
 #include <cassert>      // assert
+#include <cstdint>      // std::uint64_t
+#include <filesystem>   // std::filesystem
 #include <fstream>      // std::ifstream
+#include <istream>      // std::basic_istream
+#include <ostream>      // std::basic_ostream
 #include <system_error> // std::make_error_code, std::errc
 
 namespace sourcemeta::core {
diff --git a/src/core/json/json_value.cc b/src/core/json/json_value.cc
index 2ae9ca170..1796a507c 100644
--- a/src/core/json/json_value.cc
+++ b/src/core/json/json_value.cc
@@ -1,13 +1,20 @@
+#include <sourcemeta/core/json_array.h>
 #include <sourcemeta/core/json_value.h>
 
-#include <algorithm> // std::find
-#include <cassert>   // assert
-#include <cmath>     // std::isinf, std::isnan, std::modf, std::trunc
-#include <numeric>   // std::transform
-#include <stdexcept> // std::invalid_argument
-#include <string>    // std::to_string
-#include <utility>   // std::move
-#include <vector>    // std::vector
+#include <algorithm>        // std::find
+#include <cassert>          // assert
+#include <cmath>            // std::isinf, std::isnan, std::modf, std::trunc
+#include <cstddef>          // std::size_t
+#include <cstdint>          // std::int64_t
+#include <functional>       // std::reference_wrapper
+#include <initializer_list> // std::initializer_list
+#include <numeric>          // std::transform
+#include <sstream>          // std::basic_istringstream
+#include <stdexcept>        // std::invalid_argument
+#include <string>           // std::to_string
+#include <string_view>      // std::basic_string_view
+#include <utility>          // std::move
+#include <vector>           // std::vector
 
 namespace sourcemeta::core {
 
diff --git a/src/core/json/parser.h b/src/core/json/parser.h
index 86f2e13e9..f7def1e47 100644
--- a/src/core/json/parser.h
+++ b/src/core/json/parser.h
@@ -3,11 +3,12 @@
 
 #include "grammar.h"
 
-#include <sourcemeta/core/json.h>
 #include <sourcemeta/core/json_error.h>
+#include <sourcemeta/core/json_value.h>
 
 #include <cassert>    // assert
 #include <cctype>     // std::isxdigit
+#include <cstddef>    // std::size_t
 #include <cstdint>    // std::uint64_t
 #include <functional> // std::reference_wrapper
 #include <istream>    // std::basic_istream
diff --git a/src/core/json/stringify.h b/src/core/json/stringify.h
index 161310516..4e5b1b020 100644
--- a/src/core/json/stringify.h
+++ b/src/core/json/stringify.h
@@ -3,14 +3,18 @@
 
 #include "grammar.h"
 
-#include <sourcemeta/core/json.h>
+#include <sourcemeta/core/json_value.h>
 
 #include <algorithm> // std::transform, std::sort
+#include <cstddef>   // std::size_t
+#include <cstdint>   // std::int64_t
 #include <iomanip>   // std::setprecision
 #include <ios>       // std::noshowpoint, std::fixed
 #include <iterator>  // std::next, std::cbegin, std::cend, std::back_inserter
 #include <ostream>   // std::basic_ostream
+#include <sstream>   // std::ostringstream
 #include <string>    // std::to_string
+#include <vector>    // std::vector
 
 namespace sourcemeta::core::internal {
 constexpr auto LINE_WIDTH{80};