diff --git a/src/core/include/mp-units/unit.h b/src/core/include/mp-units/unit.h
index 79b2512a..cbcdde91 100644
--- a/src/core/include/mp-units/unit.h
+++ b/src/core/include/mp-units/unit.h
@@ -836,6 +836,11 @@ constexpr Out unit_symbol_impl(Out out, const derived_unit<Expr...>&, unit_symbo
 template<Unit auto U>
 inline constexpr bool space_before_unit_symbol = true;
 
+template<>
+inline constexpr bool space_before_unit_symbol<percent> = false;
+template<>
+inline constexpr bool space_before_unit_symbol<per_mille> = false;
+
 template<typename CharT = char, std::output_iterator<CharT> Out, Unit U>
 constexpr Out unit_symbol_to(Out out, U u, unit_symbol_formatting fmt = unit_symbol_formatting{})
 {
diff --git a/test/runtime/fmt_test.cpp b/test/runtime/fmt_test.cpp
index 71ea8588..b1d131ec 100644
--- a/test/runtime/fmt_test.cpp
+++ b/test/runtime/fmt_test.cpp
@@ -233,11 +233,11 @@ TEST_CASE("operator<< on a quantity", "[text][ostream][fmt]")
       const auto q = value_cast<percent>(15. * isq::length[m] / (100. * isq::length[m]));
       os << q;
 
-      SECTION("iostream") { CHECK(os.str() == "15 %"); }
+      SECTION("iostream") { CHECK(os.str() == "15%"); }
 
       SECTION("fmt with default format {} on a quantity") { CHECK(MP_UNITS_STD_FMT::format("{}", q) == os.str()); }
 
-      SECTION("fmt with format {:%Q %q} on a quantity") { CHECK(MP_UNITS_STD_FMT::format("{:%Q %q}", q) == os.str()); }
+      SECTION("fmt with format {:%Q %q} on a quantity") { CHECK(MP_UNITS_STD_FMT::format("{:%Q %q}", q) == "15 %"); }
     }
 
     SECTION("radians")