diff --git a/src/gmio_core/internal/string_utils.h b/src/gmio_core/internal/string_utils.h
index 01663d7..0b40e35 100644
--- a/src/gmio_core/internal/string_utils.h
+++ b/src/gmio_core/internal/string_utils.h
@@ -21,6 +21,7 @@
 /*! Returns non-zero if \p c is a space (for C-locale), zero otherwise */
 GMIO_INLINE int gmio_clocale_isspace(char c)
 {
+#if 0
     return c == 0x20      /* space (SPC) */
             || c == 0x09  /* horizontal tab (TAB) */
             || c == 0x0a  /* newline (LF) */
@@ -28,6 +29,28 @@ GMIO_INLINE int gmio_clocale_isspace(char c)
             || c == 0x0c  /* feed (FF) */
             || c == 0x0d  /* carriage return (CR) */
             ;
+    /* return c == 0x20 || ((uint8_t)(c - 0x09) < 5); */
+#else
+    static const unsigned char space_chars[] = {
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+    };
+    return space_chars[c];
+#endif
 }
 
 /*! Returns true if \p c1 compare equals to \p c2
diff --git a/tests/test_internal.c b/tests/test_internal.c
index 893165d..f5d2518 100644
--- a/tests/test_internal.c
+++ b/tests/test_internal.c
@@ -23,6 +23,7 @@
 #include "../src/gmio_core/internal/fast_atof.h"
 #include "../src/gmio_core/internal/safe_cast.h"
 #include "../src/gmio_core/internal/string_parse.h"
+#include "../src/gmio_core/internal/string_utils.h"
 
 #include "stream_buffer.h"
 #include "utils.h"
@@ -202,6 +203,17 @@ const char* test_internal__string_parse()
     return NULL;
 }
 
+const char* test_internal__string_utils()
+{
+    UTEST_ASSERT(gmio_clocale_isspace(' '));
+    UTEST_ASSERT(gmio_clocale_isspace('\t'));
+    UTEST_ASSERT(gmio_clocale_isspace('\n'));
+    UTEST_ASSERT(gmio_clocale_isspace('\r'));
+    UTEST_ASSERT(!gmio_clocale_isspace('a'));
+    UTEST_ASSERT(!gmio_clocale_isspace('A'));
+    return NULL;
+}
+
 const char* all_tests()
 {
     UTEST_SUITE_START();
@@ -210,6 +222,7 @@ const char* all_tests()
     UTEST_RUN(test_internal__fast_atof);
     UTEST_RUN(test_internal__safe_cast);
     UTEST_RUN(test_internal__string_parse);
+    UTEST_RUN(test_internal__string_utils);
     return NULL;
 }