diff --git a/base/string_utils.cpp b/base/string_utils.cpp
index f2546161fb..f90c24e7f8 100644
--- a/base/string_utils.cpp
+++ b/base/string_utils.cpp
@@ -236,6 +236,12 @@ bool IsASCIIString(std::string const & str)
 }
 
 bool IsASCIIDigit(UniChar c) { return c >= '0' && c <= '9'; }
+
+bool IsASCIISpace(UniChar c)
+{
+  return c == ' ' || c == '\f' || c == '\n' || c == '\r' || c == '\t' || c == '\v';
+}
+
 bool IsASCIILatin(UniChar c) { return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'); }
 
 bool StartsWith(UniString const & s, UniString const & p)
diff --git a/base/string_utils.hpp b/base/string_utils.hpp
index 1ebec6dc13..3e353fd3ac 100644
--- a/base/string_utils.hpp
+++ b/base/string_utils.hpp
@@ -88,6 +88,7 @@ UniString MakeUniString(std::string const & utf8s);
 std::string ToUtf8(UniString const & s);
 bool IsASCIIString(std::string const & str);
 bool IsASCIIDigit(UniChar c);
+bool IsASCIISpace(UniChar c);
 bool IsASCIILatin(UniChar c);
 
 inline std::string DebugPrint(UniString const & s) { return ToUtf8(s); }
diff --git a/indexer/search_string_utils.cpp b/indexer/search_string_utils.cpp
index 88027211d6..9a651056ff 100644
--- a/indexer/search_string_utils.cpp
+++ b/indexer/search_string_utils.cpp
@@ -5,8 +5,6 @@
 #include "base/macros.hpp"
 #include "base/mem_trie.hpp"
 
-#include <cctype>
-
 using namespace std;
 using namespace strings;
 
@@ -29,10 +27,10 @@ void RemoveNumeroSigns(UniString & s)
     }
 
     size_t j = i + 1;
-    while (j < n && isspace(s[j]))
+    while (j < n && IsASCIISpace(s[j]))
       ++j;
 
-    if (j == n || isdigit(s[j]))
+    if (j == n || IsASCIIDigit(s[j]))
       s[i] = ' ';
 
     i = j;
@@ -68,9 +66,9 @@ UniString NormalizeAndSimplifyString(string const & s)
       break;
     // Some Danish-specific hacks.
     case 0x00d8:  // Ø
-    case 0x00f8:
+    case 0x00f8:  // ø
       c = 'o';
-      break;      // ø
+      break;
     case 0x0152:  // Œ
     case 0x0153:  // œ
       c = 'o';