diff --git a/src/buffer_manager.cc b/src/buffer_manager.cc
index 37bef1bb..c830d011 100644
--- a/src/buffer_manager.cc
+++ b/src/buffer_manager.cc
@@ -103,7 +103,7 @@ CandidateList BufferManager::complete_buffername(const String& prefix,
     for (auto& buffer : m_buffers)
     {
         String name = buffer->display_name();
-        if (name.substr(0, real_prefix.length()) == real_prefix)
+        if (prefix_match(name, real_prefix))
             result.push_back(escape(name));
     }
     // no prefix completion found, check regex matching
diff --git a/src/client.cc b/src/client.cc
index ca6f047c..f43203bb 100644
--- a/src/client.cc
+++ b/src/client.cc
@@ -350,11 +350,10 @@ public:
                    m_prefix = line;
                 auto it = m_history_it;
                 // search for the previous history entry matching typed prefix
-                ByteCount prefix_length = m_prefix.length();
                 do
                 {
                     --it;
-                    if (it->substr(0, prefix_length) == m_prefix)
+                    if (prefix_match(*it, m_prefix))
                     {
                         m_history_it = it;
                         m_line_editor.reset(*it);
@@ -368,11 +367,10 @@ public:
         {
             if (m_history_it != history.end())
             {
-                ByteCount prefix_length = m_prefix.length();
                 // search for the next history entry matching typed prefix
                 ++m_history_it;
                 while (m_history_it != history.end() and
-                       m_history_it->substr(0, prefix_length) != m_prefix)
+                       prefix_match(*m_history_it, m_prefix))
                     ++m_history_it;
 
                 if (m_history_it != history.end())
diff --git a/src/command_manager.cc b/src/command_manager.cc
index c8e5d05a..c62d75fa 100644
--- a/src/command_manager.cc
+++ b/src/command_manager.cc
@@ -337,7 +337,7 @@ Completions CommandManager::complete(const Context& context,
 
         for (auto& command : m_commands)
         {
-            if (command.first.substr(0, prefix.length()) == prefix)
+            if (prefix_match(command.first, prefix))
                 result.candidates.push_back(command.first);
         }
         std::sort(result.candidates.begin(), result.candidates.end());
diff --git a/src/file.cc b/src/file.cc
index ed4a8276..e8aa87b7 100644
--- a/src/file.cc
+++ b/src/file.cc
@@ -74,7 +74,7 @@ String compact_path(const String& filename)
     char cwd[1024];
     getcwd(cwd, 1024);
     String real_cwd = real_path(cwd) + '/';
-    if (real_filename.substr(0, real_cwd.length()) == real_cwd)
+    if (prefix_match(real_filename, real_cwd))
         return real_filename.substr(real_cwd.length());
 
     const char* home = getenv("HOME");
@@ -302,7 +302,7 @@ std::vector<String> complete_filename(const String& prefix,
         if (check_ignored_regex and boost::regex_match(filename.c_str(), ignored_regex))
             continue;
 
-        const bool match_prefix = (filename.substr(0, fileprefix.length()) == fileprefix);
+        const bool match_prefix = prefix_match(filename, fileprefix);
         const bool match_regex  = not file_regex.empty() and
             boost::regex_match(filename.c_str(), file_regex);
 
diff --git a/src/idvaluemap.hh b/src/idvaluemap.hh
index 3a263c6e..9efbdd68 100644
--- a/src/idvaluemap.hh
+++ b/src/idvaluemap.hh
@@ -78,7 +78,7 @@ public:
                 continue;
 
             String id_str = value.first;
-            if (id_str.substr(0, real_prefix.length()) == real_prefix)
+            if (prefix_match(id_str, real_prefix))
                 result.push_back(std::move(id_str));
         }
         return result;
diff --git a/src/option_manager.cc b/src/option_manager.cc
index 5bca3323..daef90bb 100644
--- a/src/option_manager.cc
+++ b/src/option_manager.cc
@@ -73,8 +73,7 @@ CandidateList OptionManager::complete_option_name(const String& prefix,
     for (auto& option : m_options)
     {
         const auto& name = option->name();
-        if (name.substr(0, real_prefix.length()) == real_prefix and
-            not contains(result, name))
+        if (prefix_match(name, real_prefix) and not contains(result, name))
             result.push_back(name);
     }
     return result;
diff --git a/src/string.cc b/src/string.cc
index dcfc1037..870cdf9e 100644
--- a/src/string.cc
+++ b/src/string.cc
@@ -83,4 +83,15 @@ void option_from_string(const String& str, Regex& re)
     }
 }
 
+bool prefix_match(const String& str, const String& prefix)
+{
+    auto it = str.begin();
+    for (auto& c : prefix)
+    {
+        if (it ==str.end() or *it++ != c)
+            return false;
+    }
+    return true;
+}
+
 }
diff --git a/src/string.hh b/src/string.hh
index f4a93309..25e051dc 100644
--- a/src/string.hh
+++ b/src/string.hh
@@ -112,6 +112,8 @@ String to_string(const StronglyTypedNumber<RealType, ValueType>& val)
     return to_string((ValueType)val);
 }
 
+bool prefix_match(const String& str, const String& prefix);
+
 }
 
 namespace std
diff --git a/src/unit_tests.cc b/src/unit_tests.cc
index c0d8a15b..589a83fe 100644
--- a/src/unit_tests.cc
+++ b/src/unit_tests.cc
@@ -136,6 +136,11 @@ void test_string()
 
    String escaped = escape("youpi:matin:tchou:", ':', '\\');
    kak_assert(escaped == "youpi\\:matin\\:tchou\\:");
+
+   kak_assert(prefix_match("tchou kanaky", "tchou"));
+   kak_assert(prefix_match("tchou kanaky", "tchou kanaky"));
+   kak_assert(prefix_match("tchou kanaky", "t"));
+   kak_assert(not prefix_match("tchou kanaky", "c"));
 }
 
 void test_keys()