diff --git a/xo-arena/include/xo/arena/DCircularBuffer.hpp b/xo-arena/include/xo/arena/DCircularBuffer.hpp
index 7e49def3..c7c8abf9 100644
--- a/xo-arena/include/xo/arena/DCircularBuffer.hpp
+++ b/xo-arena/include/xo/arena/DCircularBuffer.hpp
@@ -132,12 +132,6 @@ namespace xo {
              **/
             void report_append(span_type r);
 
-            /** expand hi end of mapped memory range to at least @p hi.
-             *
-             *  Require: @p hi < @ref reserved_range_.hi
-             **/
-            bool expand_to(byte * hi);
-
             /** consume span (or prefix thereof) previously obtained from @ref occupied_range()
              *  Caller represents that it won't need to read this memory again
              *  unless overlaps with a pinned span.
@@ -162,6 +156,12 @@ namespace xo {
             /** @defgroup mm-circularbuffer-private-methods CircularBuffer non-const methods **/
             ///@{
 
+            /** expand hi end of mapped memory range to at least @p hi.
+             *
+             *  Require: @p hi < @ref reserved_range_.hi
+             **/
+            bool _expand_to(byte * hi);
+
             /** shrink occupied rnage to the smallest contiguous range that contains both:
              *  all of .input_range_, and all pinned ranges in .pinned_spans_
              **/
diff --git a/xo-arena/src/arena/DCircularBuffer.cpp b/xo-arena/src/arena/DCircularBuffer.cpp
index 9e8b28b8..70efcd2d 100644
--- a/xo-arena/src/arena/DCircularBuffer.cpp
+++ b/xo-arena/src/arena/DCircularBuffer.cpp
@@ -171,7 +171,7 @@ namespace xo {
             }
 
             /* establish mapped range at least to dest.hi */
-            this->expand_to(dest.hi());
+            this->_expand_to(dest.hi());
 
             /* report available memory */
             return span_type(occupied_range_.hi(), mapped_range_.hi());
@@ -250,38 +250,6 @@ namespace xo {
             this->_check_reset_map_start();
         }
 
-        bool
-        DCircularBuffer::expand_to(byte * hi) {
-            scope log(XO_DEBUG(config_.debug_flag_));
-
-            if (hi < mapped_range_.hi()) {
-                /* nothing todo */
-                return true;
-            }
-
-            size_t add_z = hi - mapped_range_.hi();
-            size_t add_commit_z = padding::with_padding(add_z, buffer_align_z_);
-            byte * commit_start = mapped_range_.hi();
-
-            if (::mprotect(commit_start,
-                           add_commit_z,
-                           PROT_READ | PROT_WRITE) != 0)
-                {
-                    if (log) {
-                        log("commit failed");
-                        log(xtag("commit_start", commit_start),
-                            xtag("add_z", add_z),
-                            xtag("add_commit_z", add_commit_z));
-                    }
-
-                    // this->capture_error(error::commit_failed, add_commit_z);
-                    return false;
-                }
-
-            this->mapped_range_ += span(commit_start, add_commit_z);
-            return true;
-        }
-
         void
         DCircularBuffer::pin_range(span_type r)
         {
@@ -333,6 +301,38 @@ namespace xo {
             }
         }
 
+        bool
+        DCircularBuffer::_expand_to(byte * hi) {
+            scope log(XO_DEBUG(config_.debug_flag_));
+
+            if (hi < mapped_range_.hi()) {
+                /* nothing todo */
+                return true;
+            }
+
+            size_t add_z = hi - mapped_range_.hi();
+            size_t add_commit_z = padding::with_padding(add_z, buffer_align_z_);
+            byte * commit_start = mapped_range_.hi();
+
+            if (::mprotect(commit_start,
+                           add_commit_z,
+                           PROT_READ | PROT_WRITE) != 0)
+                {
+                    if (log) {
+                        log("commit failed");
+                        log(xtag("commit_start", commit_start),
+                            xtag("add_z", add_z),
+                            xtag("add_commit_z", add_commit_z));
+                    }
+
+                    // this->capture_error(error::commit_failed, add_commit_z);
+                    return false;
+                }
+
+            this->mapped_range_ += span(commit_start, add_commit_z);
+            return true;
+        }
+
         void
         DCircularBuffer::_shrink_occupied_to_fit()
         {
diff --git a/xo-arena/utest/DCircularBuffer.test.cpp b/xo-arena/utest/DCircularBuffer.test.cpp
index debfc41f..be869478 100644
--- a/xo-arena/utest/DCircularBuffer.test.cpp
+++ b/xo-arena/utest/DCircularBuffer.test.cpp
@@ -55,6 +55,8 @@ namespace xo {
 
             REQUIRE(buf.occupied_range().to_string_view() == std::string_view("defghijklmnopq"));
         }
+
+        // TODO: test pin_range() / unpin_range()
     } /*namespace ut*/
 } /*namespace xo*/