diff --git a/src/kernel/error_msgs.cpp b/src/kernel/error_msgs.cpp
index ae2d26a1c..c76145599 100644
--- a/src/kernel/error_msgs.cpp
+++ b/src/kernel/error_msgs.cpp
@@ -7,7 +7,7 @@ Author: Leonardo de Moura
 #include "kernel/error_msgs.h"
 
 namespace lean {
-static format pp_indent_expr(formatter const & fmt, environment const & env, options const & opts, expr const & e) {
+format pp_indent_expr(formatter const & fmt, environment const & env, options const & opts, expr const & e) {
     return nest(get_pp_indent(opts), compose(line(), fmt(env, e, opts)));
 }
 
diff --git a/src/kernel/error_msgs.h b/src/kernel/error_msgs.h
index 207a2aac4..a4d1ce43a 100644
--- a/src/kernel/error_msgs.h
+++ b/src/kernel/error_msgs.h
@@ -8,6 +8,7 @@ Author: Leonardo de Moura
 #include "kernel/expr.h"
 #include "kernel/formatter.h"
 namespace lean {
+format pp_indent_expr(formatter const & fmt, environment const & env, options const & opts, expr const & e);
 format pp_type_expected(formatter const & fmt, environment const & env, options const & opts, expr const & e);
 format pp_function_expected(formatter const & fmt, environment const & env, options const & opts, expr const & e);
 format pp_app_type_mismatch(formatter const & fmt, environment const & env, options const & opts, expr const & app,