diff --git a/src/libutil/string.hh b/src/libutil/string.hh
deleted file mode 100644
index 16ef75643..000000000
--- a/src/libutil/string.hh
+++ /dev/null
@@ -1,17 +0,0 @@
-#pragma once
-
-namespace nix {
-
-    /** Locale-independent version of std::islower(). */
-    inline bool isASCIILower(char c) { return c >= 'a' && c <= 'z'; };
-
-    /** Locale-independent version of std::isupper(). */
-    inline bool isASCIIUpper(char c) { return c >= 'A' && c <= 'Z'; };
-
-    /** Locale-independent version of std::isalpha(). */
-    inline bool isASCIIAlpha(char c) { return isASCIILower(c) || isASCIIUpper(c); };
-
-    /** Locale-independent version of std::isdigit(). */
-    inline bool isASCIIDigit(char c) { return c >= '0' && c <= '9'; };
-
-}
diff --git a/tests/unit/libutil/string.cc b/tests/unit/libutil/string.cc
deleted file mode 100644
index 381f2cc15..000000000
--- a/tests/unit/libutil/string.cc
+++ /dev/null
@@ -1,59 +0,0 @@
-#include <gtest/gtest.h>
-#include "string.hh"
-
-namespace nix {
-
-TEST(string, isASCIILower) {
-    ASSERT_TRUE(isASCIILower('a'));
-    ASSERT_TRUE(isASCIILower('z'));
-    ASSERT_FALSE(isASCIILower('A'));
-    ASSERT_FALSE(isASCIILower('Z'));
-    ASSERT_FALSE(isASCIILower('0'));
-    ASSERT_FALSE(isASCIILower('9'));
-    ASSERT_FALSE(isASCIILower(' '));
-    ASSERT_FALSE(isASCIILower('\n'));
-    ASSERT_FALSE(isASCIILower('\t'));
-    ASSERT_FALSE(isASCIILower(':'));
-}
-
-TEST(string, isASCIIUpper) {
-    ASSERT_FALSE(isASCIIUpper('a'));
-    ASSERT_FALSE(isASCIIUpper('z'));
-    ASSERT_TRUE(isASCIIUpper('A'));
-    ASSERT_TRUE(isASCIIUpper('Z'));
-    ASSERT_FALSE(isASCIIUpper('0'));
-    ASSERT_FALSE(isASCIIUpper('9'));
-    ASSERT_FALSE(isASCIIUpper(' '));
-    ASSERT_FALSE(isASCIIUpper('\n'));
-    ASSERT_FALSE(isASCIIUpper('\t'));
-    ASSERT_FALSE(isASCIIUpper(':'));
-}
-
-TEST(string, isASCIIAlpha) {
-    ASSERT_TRUE(isASCIIAlpha('a'));
-    ASSERT_TRUE(isASCIIAlpha('z'));
-    ASSERT_TRUE(isASCIIAlpha('A'));
-    ASSERT_TRUE(isASCIIAlpha('Z'));
-    ASSERT_FALSE(isASCIIAlpha('0'));
-    ASSERT_FALSE(isASCIIAlpha('9'));
-    ASSERT_FALSE(isASCIIAlpha(' '));
-    ASSERT_FALSE(isASCIIAlpha('\n'));
-    ASSERT_FALSE(isASCIIAlpha('\t'));
-    ASSERT_FALSE(isASCIIAlpha(':'));
-}
-
-TEST(string, isASCIIDigit) {
-    ASSERT_FALSE(isASCIIDigit('a'));
-    ASSERT_FALSE(isASCIIDigit('z'));
-    ASSERT_FALSE(isASCIIDigit('A'));
-    ASSERT_FALSE(isASCIIDigit('Z'));
-    ASSERT_TRUE(isASCIIDigit('0'));
-    ASSERT_TRUE(isASCIIDigit('1'));
-    ASSERT_TRUE(isASCIIDigit('9'));
-    ASSERT_FALSE(isASCIIDigit(' '));
-    ASSERT_FALSE(isASCIIDigit('\n'));
-    ASSERT_FALSE(isASCIIDigit('\t'));
-    ASSERT_FALSE(isASCIIDigit(':'));
-}
-
-}
\ No newline at end of file