diff --git a/CMakeLists.txt b/CMakeLists.txt
index b1358d1..f2d1233 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -452,7 +452,6 @@ if(NOT SNMALLOC_HEADER_ONLY_LIBRARY)
     if (WIN32
     OR (CMAKE_SYSTEM_NAME STREQUAL NetBSD)
     OR (CMAKE_SYSTEM_NAME STREQUAL OpenBSD)
-    OR (CMAKE_SYSTEM_NAME STREQUAL DragonFly)
     OR (CMAKE_SYSTEM_NAME STREQUAL SunOS))
     # Windows does not support aligned allocation well enough
     # for pass through.
diff --git a/src/snmalloc/mem/external_alloc.h b/src/snmalloc/mem/external_alloc.h
index 4eecfa9..2507197 100644
--- a/src/snmalloc/mem/external_alloc.h
+++ b/src/snmalloc/mem/external_alloc.h
@@ -45,6 +45,11 @@ namespace snmalloc::external_alloc
 {
   using ::malloc_usable_size;
 }
+#    elif defined(__DragonFly__)
+namespace snmalloc::external_alloc
+{
+  using ::malloc_usable_size;
+}
 #    else
 #      error Define malloc size macro for this platform.
 #    endif