diff --git a/src/c/reader.d b/src/c/reader.d
index 7605158fc..cc58747f2 100644
--- a/src/c/reader.d
+++ b/src/c/reader.d
@@ -92,34 +92,7 @@ ecl_invalid_character_p(int c)
   return (c <= 32) || (c == 127);
 }
 
-/* -- tokens ---------------------------------------------------------------- */
-
-static cl_object
-ecl_make_token()
-{
-  cl_object o = ecl_alloc_object(t_token);
-  o->token.escaped = 0;
-  o->token.string = si_get_buffer_string();
-  o->token.escape = ecl_make_stack(0);
-  return o;
-}
-
-cl_object
-si_token_string(cl_object token)
-{
-  cl_env_ptr the_env = ecl_process_env();
-  cl_object object = token->token.string;
-  ecl_return1(the_env, object);
-}
-
-cl_object
-si_token_escape(cl_object token)
-{
-  cl_env_ptr the_env = ecl_process_env();
-  cl_object object = token->token.escape;
-  ecl_return1(the_env, object);
-}
-
+/* -- buffer ---------------------------------------------------------------- */
 cl_object
 si_get_buffer_string()
 {
@@ -160,6 +133,82 @@ si_put_buffer_string(cl_object string)
   @(return);
 }
 
+/* INV the buffer is never simultenaously used nor does it have displacements,
+   so we can open-code PUSH-EXTEND and eagerly deallocate the underlying array.
+   -- jd 2026-03-08 */
+static ecl_character
+_ecl_string_push_extend(cl_object s, ecl_character c)
+{
+  cl_index dim, fillp;
+  switch(ecl_t_of(s)) {
+#ifdef ECL_UNICODE
+  case t_string:
+    fillp = s->string.fillp;
+    dim = s->string.dim;
+    if (fillp >= dim) {
+      cl_index new_size = dim + dim/2 + 1;
+      cl_index old_bytes = sizeof(ecl_character) * dim;
+      cl_index new_bytes = sizeof(ecl_character) * new_size;
+      ecl_character *old_self = s->string.self;
+      ecl_character *new_self = (ecl_character *)ecl_alloc_atomic(new_bytes);
+      ecl_copy(new_self, old_self, old_bytes);
+      s->string.self = new_self;
+      s->string.dim = new_size;
+      ecl_dealloc(old_self);
+    }
+    s->string.fillp++;
+    return s->string.self[fillp] = c;
+#endif
+  case t_base_string:
+    fillp = s->base_string.fillp;
+    dim = s->base_string.dim;
+    if (fillp >= dim) {
+      cl_index new_size = dim + dim/2 + 1;
+      cl_index old_bytes = sizeof(ecl_base_char) * dim;
+      cl_index new_bytes = sizeof(ecl_base_char) * new_size;
+      ecl_base_char *old_self = s->base_string.self;
+      ecl_base_char *new_self = (ecl_base_char *)ecl_alloc_atomic(new_bytes+1);
+      new_self[new_bytes] = 0;
+      ecl_copy(new_self, old_self, old_bytes);
+      s->base_string.self = new_self;
+      s->base_string.dim = new_size;
+      ecl_dealloc(old_self);
+    }
+    s->base_string.fillp++;
+    return s->base_string.self[fillp] = c;
+  default:
+    ecl_internal_error("BUFFER-STRING is not a string.");
+  }
+}
+
+/* -- tokens ---------------------------------------------------------------- */
+
+static cl_object
+ecl_make_token()
+{
+  cl_object o = ecl_alloc_object(t_token);
+  o->token.escaped = 0;
+  o->token.string = si_get_buffer_string();
+  o->token.escape = ecl_make_stack(0);
+  return o;
+}
+
+cl_object
+si_token_string(cl_object token)
+{
+  cl_env_ptr the_env = ecl_process_env();
+  cl_object object = token->token.string;
+  ecl_return1(the_env, object);
+}
+
+cl_object
+si_token_escape(cl_object token)
+{
+  cl_env_ptr the_env = ecl_process_env();
+  cl_object object = token->token.escape;
+  ecl_return1(the_env, object);
+}
+
 /* FIXME pools should be resizeable stacks. */
 cl_object
 ecl_get_reader_token(void)
@@ -237,7 +286,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
     if (a == cat_single_escape) {
       c = ecl_read_char_noeof(in);
       a = cat_constituent;
-      ecl_string_push_extend(string, c);
+      _ecl_string_push_extend(string, c);
       length++;
       ecl_stack_push(escape, ecl_make_fixnum(length-1));
       ecl_stack_push(escape, ecl_make_fixnum(length));
@@ -253,7 +302,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
           a = cat_constituent;
         } else if (a == cat_multiple_escape)
           break;
-        ecl_string_push_extend(string, c);
+        _ecl_string_push_extend(string, c);
         length++;
       }
       ecl_stack_push(escape, ecl_make_fixnum(begin));
@@ -280,7 +329,7 @@ ecl_read_token(cl_object rtbl, cl_object in, int flags)
           c = ecl_char_upcase(c);
       }
     }
-    ecl_string_push_extend(string, c);
+    _ecl_string_push_extend(string, c);
     length++;
   NEXT:
     c = ecl_read_char(in);