diff --git a/src/sink/GEAR/sink_io.h b/src/sink/GEAR/sink_io.h
index fe86573da2656253910489946350e2aa42b3e3da..79a427be5d705c1c3d30d96eaaca06bdffc3453a 100644
--- a/src/sink/GEAR/sink_io.h
+++ b/src/sink/GEAR/sink_io.h
@@ -127,7 +127,7 @@ INLINE static void sink_write_particles(const struct sink* sinks,
                                         int with_cosmology) {
 
   /* Say how much we want to write */
-  *num_fields = 10;
+  *num_fields = 11;
 
   /* List what we want to write */
   list[0] = io_make_output_field_convert_sink(
@@ -179,12 +179,12 @@ INLINE static void sink_write_particles(const struct sink* sinks,
       "Physical swallowed angular momentum of the particles");
 
   if (with_cosmology) {
-    list[9] = io_make_physical_output_field(
+    list[10] = io_make_physical_output_field(
         "BirthScaleFactors", FLOAT, 1, UNIT_CONV_NO_UNITS, 0.f, sinks,
         birth_scale_factor, /*can convert to comoving=*/0,
         "Scale-factors at which the sinks were born");
   } else {
-    list[9] =
+    list[10] =
         io_make_output_field("BirthTimes", FLOAT, 1, UNIT_CONV_TIME, 0.f, sinks,
                              birth_time, "Times at which the sinks were born");
   }