diff --git a/src/core/include/mp-units/bits/fmt.h b/src/core/include/mp-units/bits/fmt.h
index 3e59cc03..c4848d67 100644
--- a/src/core/include/mp-units/bits/fmt.h
+++ b/src/core/include/mp-units/bits/fmt.h
@@ -36,6 +36,7 @@
 
 #ifndef MP_UNITS_IN_MODULE_INTERFACE
 #include <gsl/gsl-lite.hpp>
+#include <array>
 #include <concepts>
 #include <cstdint>
 #include <limits>
diff --git a/test/static/fixed_string_test.cpp b/test/static/fixed_string_test.cpp
index 87ca7660..f1885e0c 100644
--- a/test/static/fixed_string_test.cpp
+++ b/test/static/fixed_string_test.cpp
@@ -21,6 +21,7 @@
 // SOFTWARE.
 
 #include <mp-units/ext/fixed_string.h>
+#include <array>
 #include <string_view>
 
 using namespace mp_units;