diff --git a/Makefile b/Makefile
index 0ba011e2a..05c4bdc8a 100644
--- a/Makefile
+++ b/Makefile
@@ -17,7 +17,8 @@ makefiles = \
   misc/upstart/local.mk \
   doc/manual/local.mk \
   tests/local.mk \
-  tests/plugins/local.mk
+  tests/plugins/local.mk \
+  src/error-demo/local.mk
 
 -include Makefile.config
 
diff --git a/src/error-demo/error-demo.cc b/src/error-demo/error-demo.cc
index 82e9f0580..0216092e3 100644
--- a/src/error-demo/error-demo.cc
+++ b/src/error-demo/error-demo.cc
@@ -1,5 +1,6 @@
 #include "logging.hh"
 #include "nixexpr.hh"
+#include "util.hh"
 
 #include <iostream>
 #include <optional>
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index e4f45a2d3..0765a2945 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -182,7 +182,7 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
     }
 
     // lines of code.
-    if (einfo.nixCode.has_value()) {
+    if (einfo.nixCode.has_value() && einfo.nixCode->errLineOfCode.has_value()) {
         printCodeLines(out, prefix, *einfo.nixCode);
         out << prefix << std::endl;
     }