diff --git a/src/hb-dsalgs.hh b/src/hb-dsalgs.hh
index dccca3cf9..1956bb9ba 100644
--- a/src/hb-dsalgs.hh
+++ b/src/hb-dsalgs.hh
@@ -588,16 +588,15 @@ struct hb_array_t
 
   inline unsigned int get_size (void) const { return len * sizeof (Type); }
 
-  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *seg_count /* IN/OUT */) const
+  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *seg_count = nullptr /* IN/OUT */) const
   {
-    if (!seg_count) return hb_array_t<Type> ();
-
     unsigned int count = len;
     if (unlikely (start_offset > count))
       count = 0;
     else
       count -= start_offset;
-    count = *seg_count = MIN (count, *seg_count);
+    if (seg_count)
+      count = *seg_count = MIN (count, *seg_count);
     return hb_array_t<Type> (arrayZ + start_offset, count);
   }
   inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int seg_count) const
diff --git a/src/hb-open-type.hh b/src/hb-open-type.hh
index 69cc5ccf3..b9d917d3b 100644
--- a/src/hb-open-type.hh
+++ b/src/hb-open-type.hh
@@ -541,11 +541,11 @@ struct ArrayOf
 
   inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int count) const
   { return as_array ().sub_array (start_offset, count);}
-  inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int *count /* IN/OUT */) const
+  inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int *count = nullptr /* IN/OUT */) const
   { return as_array ().sub_array (start_offset, count);}
   inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int count)
   { return as_array ().sub_array (start_offset, count);}
-  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *count /* IN/OUT */)
+  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *count = nullptr /* IN/OUT */)
   { return as_array ().sub_array (start_offset, count);}
 
   inline bool serialize (hb_serialize_context_t *c,
@@ -812,11 +812,11 @@ struct SortedArrayOf : ArrayOf<Type, LenType>
 
   inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int count) const
   { return as_array ().sub_array (start_offset, count);}
-  inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int *count /* IN/OUT */) const
+  inline hb_array_t<const Type> sub_array (unsigned int start_offset, unsigned int *count = nullptr /* IN/OUT */) const
   { return as_array ().sub_array (start_offset, count);}
   inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int count)
   { return as_array ().sub_array (start_offset, count);}
-  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *count /* IN/OUT */)
+  inline hb_array_t<Type> sub_array (unsigned int start_offset, unsigned int *count = nullptr /* IN/OUT */)
   { return as_array ().sub_array (start_offset, count);}
 
   template <typename T>