diff --git a/tests/unit/helpers/random_string.cpp b/tests/unit/helpers/random_string.cpp
index d4c8ca5cd3c2ecd5cbad1947811121039bed2c94..223a70e9e9e3adf82802aedd1be2e730ca8cb879 100644
--- a/tests/unit/helpers/random_string.cpp
+++ b/tests/unit/helpers/random_string.cpp
@@ -41,7 +41,7 @@ random_string(std::size_t length) {
 
     thread_local static std::mt19937 rng{std::random_device{}()};
     thread_local static std::uniform_int_distribution<std::string::size_type>
-            pick(0, std::size(charset) - 1);
+            pick(0, std::size(charset) - 2);
 
     std::string s(length, '\0');
 
diff --git a/tests/unit/test_helpers.cpp b/tests/unit/test_helpers.cpp
index 27d90e6b4207dd37e4da1c8f0e3ee3c6b0f7b197..c606931d05f0a532ad97ffb9e8ad82b085a56473 100644
--- a/tests/unit/test_helpers.cpp
+++ b/tests/unit/test_helpers.cpp
@@ -45,10 +45,11 @@ SCENARIO("random strings can be generated", "[test_helpers][random_string]") {
 
         WHEN("Length is a positive integer") {
 
-            const auto s = helpers::random_string(6);
+            const std::size_t n = GENERATE(range(1, 5432));
+            const auto s = helpers::random_string(n);
 
             THEN(" The generated string is empty ") {
-                REQUIRE(s.length() == 6);
+                REQUIRE(s.length() == n);
             }
         }
     }