diff --git a/src/lib/icu/Util.cxx b/src/lib/icu/Util.cxx
index 57cf2f59f..bd276756a 100644
--- a/src/lib/icu/Util.cxx
+++ b/src/lib/icu/Util.cxx
@@ -27,6 +27,7 @@
 #include <unicode/ustring.h>
 
 #include <memory>
+#include <stdexcept>
 
 #include <assert.h>
 #include <string.h>
@@ -73,3 +74,25 @@ UCharToUTF8(ConstBuffer<UChar> src)
 	dest[dest_length] = 0;
 	return AllocatedString<>::Donate(dest.release());
 }
+
+AllocatedString<>
+UCharToUTF8Throw(ConstBuffer<UChar> src)
+{
+	assert(!src.IsNull());
+
+	/* worst-case estimate */
+	size_t dest_capacity = 4 * src.size;
+
+	std::unique_ptr<char[]> dest(new char[dest_capacity + 1]);
+
+	UErrorCode error_code = U_ZERO_ERROR;
+	int32_t dest_length;
+	u_strToUTF8(dest.get(), dest_capacity, &dest_length,
+		    src.data, src.size,
+		    &error_code);
+	if (U_FAILURE(error_code))
+		throw std::runtime_error(u_errorName(error_code));
+
+	dest[dest_length] = 0;
+	return AllocatedString<>::Donate(dest.release());
+}
diff --git a/src/lib/icu/Util.hxx b/src/lib/icu/Util.hxx
index e2dd3713c..c72d6330f 100644
--- a/src/lib/icu/Util.hxx
+++ b/src/lib/icu/Util.hxx
@@ -40,4 +40,12 @@ UCharFromUTF8(const char *src);
 AllocatedString<char>
 UCharToUTF8(ConstBuffer<UChar> src);
 
+/**
+ * Wrapper for u_strToUTF8().
+ *
+ * Throws std::runtime_error on error.
+ */
+AllocatedString<char>
+UCharToUTF8Throw(ConstBuffer<UChar> src);
+
 #endif