diff --git a/src/averaged_perceptron_trainer.h b/src/averaged_perceptron_trainer.h
index aad0488b..a4c22e7b 100644
--- a/src/averaged_perceptron_trainer.h
+++ b/src/averaged_perceptron_trainer.h
@@ -78,7 +78,7 @@ bool averaged_perceptron_trainer_train_example(averaged_perceptron_trainer_t *se
                                                cstring_array *features,
                                                cstring_array *prev_tag_features,
                                                cstring_array *prev2_tag_features,
-                                               ap_tagger_feature_function feature_function,
+                                               tagger_feature_function feature_function,
                                                tokenized_string_t *tokenized,
                                                cstring_array *labels
                                                );
diff --git a/src/tagger.h b/src/tagger.h
new file mode 100644
index 00000000..650c66e0
--- /dev/null
+++ b/src/tagger.h
@@ -0,0 +1,5 @@
+#include "string_utils.h"
+#include "tokens.h"
+
+// Arguments:                           tagger, context, tokenized str,       index
+typedef bool (*tagger_feature_function)(void *, void *, tokenized_string_t *, uint32_t);
\ No newline at end of file