diff --git a/src/libespeak-ng/setlengths.c b/src/libespeak-ng/setlengths.c
index 367cd883..923d4456 100644
--- a/src/libespeak-ng/setlengths.c
+++ b/src/libespeak-ng/setlengths.c
@@ -29,6 +29,7 @@
 #include <espeak-ng/encoding.h>
 
 #include "readclause.h"
+#include "setlengths.h"
 
 #include "phoneme.h"
 #include "voice.h"
diff --git a/src/libespeak-ng/setlengths.h b/src/libespeak-ng/setlengths.h
new file mode 100644
index 00000000..7835c68f
--- /dev/null
+++ b/src/libespeak-ng/setlengths.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2005 to 2015 by Jonathan Duddington
+ * email: jonsd@users.sourceforge.net
+ * Copyright (C) 2015-2018 Reece H. Dunn
+ * Copyright (C) 2018 Juho Hiltunen
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see: <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef ESPEAK_NG_SETLENGTHS_H
+#define ESPEAK_NG_SETLENGTHS_H
+
+#include "translate.h"
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+void CalcLengths(Translator *tr);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
diff --git a/src/libespeak-ng/synthesize.c b/src/libespeak-ng/synthesize.c
index 775aaa7e..e778ae35 100644
--- a/src/libespeak-ng/synthesize.c
+++ b/src/libespeak-ng/synthesize.c
@@ -33,6 +33,7 @@
 #include <espeak-ng/encoding.h>
 
 #include "intonation.h"
+#include "setlengths.h"
 
 #include "phoneme.h"
 #include "voice.h"
diff --git a/src/libespeak-ng/translate.h b/src/libespeak-ng/translate.h
index 62c9bf36..13839be7 100644
--- a/src/libespeak-ng/translate.h
+++ b/src/libespeak-ng/translate.h
@@ -742,8 +742,6 @@ void MakePhonemeList(Translator *tr, int post_pause, bool new_sentence);
 void ApplySpecialAttribute2(Translator *tr, char *phonemes, int dict_flags);
 void AppendPhonemes(Translator *tr, char *string, int size, const char *ph);
 
-void CalcLengths(Translator *tr);
-
 int RemoveEnding(Translator *tr, char *word, int end_type, char *word_copy);
 int Unpronouncable(Translator *tr, char *word, int posn);
 void SetWordStress(Translator *tr, char *output, unsigned int *dictionary_flags, int tonic, int prev_stress);