diff --git a/src/systems/si-hep/include/units/isq/si/hep/momentum.h b/src/systems/si-hep/include/units/isq/si/hep/momentum.h
index 9b53b4c2..c6791501 100644
--- a/src/systems/si-hep/include/units/isq/si/hep/momentum.h
+++ b/src/systems/si-hep/include/units/isq/si/hep/momentum.h
@@ -32,13 +32,12 @@
 #include <units/isq/si/speed.h>
 #include <units/unit.h>
 
-namespace units::isq::si::hep {
-
-
 // Necessary to factor `5'344'285'992'678`, which appears in the value for eV/c.
 template<>
 inline constexpr std::optional<std::intmax_t> units::known_first_factor<296'904'777'371> = 157'667;
 
+namespace units::isq::si::hep {
+
 struct kilogram_metre_per_second : derived_unit<kilogram_metre_per_second> {};
 
 struct eV_per_c :