diff --git a/src/core/include/mp-units/bits/expression_template.h b/src/core/include/mp-units/bits/expression_template.h
index e6698b25..5ee18b62 100644
--- a/src/core/include/mp-units/bits/expression_template.h
+++ b/src/core/include/mp-units/bits/expression_template.h
@@ -27,6 +27,10 @@
 #include <mp-units/bits/external/type_traits.h>
 #include <mp-units/bits/ratio.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <cstdint>
+#endif
+
 namespace mp_units {
 
 /**
diff --git a/src/core/include/mp-units/bits/external/math_concepts.h b/src/core/include/mp-units/bits/external/math_concepts.h
index 7b95dfd4..087ea485 100644
--- a/src/core/include/mp-units/bits/external/math_concepts.h
+++ b/src/core/include/mp-units/bits/external/math_concepts.h
@@ -22,10 +22,6 @@
 
 #pragma once
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <cstdint>
-#endif
-
 namespace mp_units::detail {
 
 template<auto N>
diff --git a/src/core/include/mp-units/bits/symbol_text.h b/src/core/include/mp-units/bits/symbol_text.h
index 52a94c6a..e28d4cde 100644
--- a/src/core/include/mp-units/bits/symbol_text.h
+++ b/src/core/include/mp-units/bits/symbol_text.h
@@ -31,7 +31,6 @@
 #include <gsl/gsl-lite.hpp>
 #include <compare>
 #include <cstddef>
-#include <cstdint>
 #endif
 
 #if __cpp_lib_text_encoding
diff --git a/src/core/include/mp-units/bits/text_tools.h b/src/core/include/mp-units/bits/text_tools.h
index 22445a66..35ab0c4c 100644
--- a/src/core/include/mp-units/bits/text_tools.h
+++ b/src/core/include/mp-units/bits/text_tools.h
@@ -27,6 +27,10 @@
 #include <mp-units/bits/ratio.h>
 #include <mp-units/bits/symbol_text.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <cstdint>
+#endif
+
 namespace mp_units {
 
 namespace detail {
diff --git a/src/core/include/mp-units/dimension.h b/src/core/include/mp-units/dimension.h
index c84da48a..ae5d233d 100644
--- a/src/core/include/mp-units/dimension.h
+++ b/src/core/include/mp-units/dimension.h
@@ -33,6 +33,7 @@
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
 #include <array>
+#include <cstdint>
 #include <iterator>
 #include <string>
 #include <string_view>
diff --git a/src/core/include/mp-units/format.h b/src/core/include/mp-units/format.h
index 061f676c..f3ff7e50 100644
--- a/src/core/include/mp-units/format.h
+++ b/src/core/include/mp-units/format.h
@@ -29,10 +29,6 @@
 #include <mp-units/quantity.h>
 #include <mp-units/unit.h>
 
-#ifndef MP_UNITS_IN_MODULE_INTERFACE
-#include <cstdint>
-#endif
-
 namespace mp_units::detail {
 
 template<typename Char>
@@ -409,6 +405,7 @@ class MP_UNITS_STD_FMT::formatter<mp_units::quantity<Reference, Rep>, Char> {
     if (*begin++ != ':') throw MP_UNITS_STD_FMT::format_error("`defaults-specs` should start with a `:`");
     do {
       auto c = *begin++;
+      // TODO check if not repeated
       switch (c) {
         case 'N':
           begin = parse_default_spec(begin, end, rep_formatter_, rep_format_str_);
diff --git a/src/core/include/mp-units/ostream.h b/src/core/include/mp-units/ostream.h
index cbd816d8..ec30ba66 100644
--- a/src/core/include/mp-units/ostream.h
+++ b/src/core/include/mp-units/ostream.h
@@ -29,6 +29,7 @@
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <sstream>
+#include <cstdint>
 #endif
 
 namespace mp_units {
diff --git a/src/core/include/mp-units/quantity_spec.h b/src/core/include/mp-units/quantity_spec.h
index a43c03ad..c75725b2 100644
--- a/src/core/include/mp-units/quantity_spec.h
+++ b/src/core/include/mp-units/quantity_spec.h
@@ -38,6 +38,7 @@
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <tuple>
+#include <cstdint>
 #endif
 
 namespace mp_units {
diff --git a/src/core/include/mp-units/reference.h b/src/core/include/mp-units/reference.h
index c1fa8b95..7b37c4e9 100644
--- a/src/core/include/mp-units/reference.h
+++ b/src/core/include/mp-units/reference.h
@@ -28,6 +28,10 @@
 #include <mp-units/bits/reference_concepts.h>
 #include <mp-units/bits/representation_concepts.h>
 
+#ifndef MP_UNITS_IN_MODULE_INTERFACE
+#include <cstdint>
+#endif
+
 namespace mp_units {
 
 namespace detail {
diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/unit.h
index 703bd019..b703d9e1 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/unit.h
@@ -41,6 +41,7 @@
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
 #include <array>
+#include <cstdint>
 #include <iterator>
 #include <string>
 #include <string_view>
diff --git a/src/systems/include/mp-units/systems/hep/hep.h b/src/systems/include/mp-units/systems/hep/hep.h
index 024b3934..a2dd17bf 100644
--- a/src/systems/include/mp-units/systems/hep/hep.h
+++ b/src/systems/include/mp-units/systems/hep/hep.h
@@ -27,6 +27,7 @@
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <mp-units/unit.h>
+#include <cstdint>
 #endif
 
 MP_UNITS_EXPORT
diff --git a/test/runtime/fmt_test.cpp b/test/runtime/fmt_test.cpp
index c7603238..d1a27028 100644
--- a/test/runtime/fmt_test.cpp
+++ b/test/runtime/fmt_test.cpp
@@ -23,6 +23,7 @@
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers_exception.hpp>
 #include <mp-units/compat_macros.h>
+#include <cstdint>
 #include <iomanip>
 #include <limits>
 #include <locale>
diff --git a/test/static/quantity_point_test.cpp b/test/static/quantity_point_test.cpp
index 5be92922..f9d4e314 100644
--- a/test/static/quantity_point_test.cpp
+++ b/test/static/quantity_point_test.cpp
@@ -25,6 +25,7 @@
 #include <mp-units/systems/isq/isq.h>
 #include <mp-units/systems/si/si.h>
 #include <mp-units/systems/usc/usc.h>
+#include <cstdint>
 #include <limits>
 #include <type_traits>
 #include <utility>
diff --git a/test/static/quantity_test.cpp b/test/static/quantity_test.cpp
index dd1152ba..5635622b 100644
--- a/test/static/quantity_test.cpp
+++ b/test/static/quantity_test.cpp
@@ -25,6 +25,7 @@
 #include <mp-units/systems/isq/mechanics.h>
 #include <mp-units/systems/isq/space_and_time.h>
 #include <mp-units/systems/si/si.h>
+#include <cstdint>
 #include <limits>
 #include <utility>