diff --git a/Makefile.am b/Makefile.am
index 08e08c012..fd14b6187 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -424,6 +424,7 @@ libutil_a_SOURCES = \
 	src/util/StringBuffer.hxx \
 	src/util/StringPointer.hxx \
 	src/util/StringView.cxx src/util/StringView.hxx \
+	src/util/ConcatString.hxx \
 	src/util/AllocatedString.cxx src/util/AllocatedString.hxx \
 	src/util/StringUtil.cxx src/util/StringUtil.hxx \
 	src/util/StringCompare.cxx src/util/StringCompare.hxx \
diff --git a/src/util/Alloc.cxx b/src/util/Alloc.cxx
index 434f90df5..115dc96bb 100644
--- a/src/util/Alloc.cxx
+++ b/src/util/Alloc.cxx
@@ -19,6 +19,7 @@
 
 #include "config.h"
 #include "Alloc.hxx"
+#include "ConcatString.hxx"
 
 #include <stdlib.h>
 #include <string.h>
@@ -76,35 +77,6 @@ xstrndup(const char *s, size_t n)
 	return p;
 }
 
-template<typename... Args>
-static inline size_t
-FillLengths(size_t *lengths, const char *a, Args&&... args)
-{
-	return FillLengths(lengths, a) + FillLengths(lengths + 1, args...);
-}
-
-template<>
-inline size_t
-FillLengths(size_t *lengths, const char *a)
-{
-	return *lengths = strlen(a);
-}
-
-template<typename... Args>
-static inline void
-StringCat(char *p, const size_t *lengths, const char *a, Args&&... args)
-{
-	StringCat(p, lengths, a);
-	StringCat(p + *lengths, lengths + 1, args...);
-}
-
-template<>
-inline void
-StringCat(char *p, const size_t *lengths, const char *a)
-{
-	memcpy(p, a, *lengths);
-}
-
 template<typename... Args>
 gcc_malloc gcc_nonnull_all
 static inline char *
diff --git a/src/util/ConcatString.hxx b/src/util/ConcatString.hxx
new file mode 100644
index 000000000..7e63238f5
--- /dev/null
+++ b/src/util/ConcatString.hxx
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2014-2017 Max Kellermann <max.kellermann@gmail.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef CONCAT_STRING_HXX
+#define CONCAT_STRING_HXX
+
+#include <string.h>
+
+template<typename... Args>
+size_t
+FillLengths(size_t *lengths, const char *a, Args&&... args)
+{
+	return FillLengths(lengths, a) + FillLengths(lengths + 1, args...);
+}
+
+template<>
+size_t
+FillLengths(size_t *lengths, const char *a)
+{
+	return *lengths = strlen(a);
+}
+
+template<typename... Args>
+void
+StringCat(char *p, const size_t *lengths, const char *a, Args&&... args)
+{
+	StringCat(p, lengths, a);
+	StringCat(p + *lengths, lengths + 1, args...);
+}
+
+template<>
+void
+StringCat(char *p, const size_t *lengths, const char *a)
+{
+	memcpy(p, a, *lengths);
+}
+
+#endif