diff --git a/graf3d/g3d/src/X3DBuffer.c b/builtins/x3d/X3DBuffer.c
similarity index 99%
rename from graf3d/g3d/src/X3DBuffer.c
rename to builtins/x3d/X3DBuffer.c
index a90bcb309a9a1..886a61a25e8c5 100644
--- a/graf3d/g3d/src/X3DBuffer.c
+++ b/builtins/x3d/X3DBuffer.c
@@ -2,7 +2,7 @@
 /* Author: Nenad Buncic   13/12/95*/
 
 #include "X3DBuffer.h"
-#include "../../x3d/src/X3DDefs.h"
+#include "X3DDefs.h"
 #include <stdio.h>
 #include <stdlib.h>
 
diff --git a/builtins/x3d/X3DBuffer.h b/builtins/x3d/X3DBuffer.h
new file mode 100644
index 0000000000000..879b2f5e96a8c
--- /dev/null
+++ b/builtins/x3d/X3DBuffer.h
@@ -0,0 +1,41 @@
+/* Author: Nenad Buncic   13/12/95*/
+
+/*************************************************************************
+ * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
+ * All rights reserved.                                                  *
+ *                                                                       *
+ * For the licensing terms see $ROOTSYS/LICENSE.                         *
+ * For the list of contributors see $ROOTSYS/README/CREDITS.             *
+ *************************************************************************/
+
+#ifndef ROOT_X3DBuffer
+#define ROOT_X3DBuffer
+
+typedef struct _x3d_data_ {
+   int  numPoints;
+   int  numSegs;
+   int  numPolys;
+   float *points; /* x0, y0, z0, x1, y1, z1, ..... ..... ....    */
+   int *segs;     /* c0, p0, q0, c1, p1, q1, ..... ..... ....    */
+   int *polys;    /* c0, n0, s0, s1, ... sn, c1, n1, s0, ... sn  */
+} X3DBuffer;
+
+typedef struct _x3d_sizeof_ {
+   int  numPoints;
+   int  numSegs;
+   int  numPolys;
+} Size3D;
+
+#ifdef __cplusplus
+extern "C" int AllocateX3DBuffer ();
+extern "C" void FillX3DBuffer (X3DBuffer *buff);
+extern "C" Size3D* gFuncSize3D();
+#else
+extern int AllocateX3DBuffer ();
+extern void FillX3DBuffer (X3DBuffer *buff);
+extern Size3D* gFuncSize3D();
+#endif
+
+#define gSize3D (*gFuncSize3D())
+
+#endif
diff --git a/graf3d/x3d/src/X3DDefs.h b/builtins/x3d/X3DDefs.h
similarity index 98%
rename from graf3d/x3d/src/X3DDefs.h
rename to builtins/x3d/X3DDefs.h
index a1c4df706fb57..deb30b982e5a6 100644
--- a/graf3d/x3d/src/X3DDefs.h
+++ b/builtins/x3d/X3DDefs.h
@@ -1,5 +1,3 @@
-/* @(#)root/g3d:$Id$ */
-
 /*************************************************************************
  * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
  * All rights reserved.                                                  *
diff --git a/cmake/unix/module.modulemap b/cmake/unix/module.modulemap
index 8dca6f5787f7f..0c013e9e85c54 100644
--- a/cmake/unix/module.modulemap
+++ b/cmake/unix/module.modulemap
@@ -45,14 +45,5 @@ module ROOT_Foundation_Stage1_NoRTTI  {
   export *
 }
 
-// We have a few c files scattered all over graf3d. We need to have a module
-// which is built in C mode, to prevent trying to build the entire Graf3d module
-// within a C context.
-module "Graf3D.X3DBuffer.h_C" {
-  requires !cplusplus
-  header "X3DBuffer.h"
-  export *
-}
-
 // From this point on the contents of this file are automatically generated.
 @ROOT_GENERATED_MODULEMAP_CONTENT@
diff --git a/graf3d/g3d/CMakeLists.txt b/graf3d/g3d/CMakeLists.txt
index 7fa08352593ac..cf37fc27ff589 100644
--- a/graf3d/g3d/CMakeLists.txt
+++ b/graf3d/g3d/CMakeLists.txt
@@ -27,10 +27,11 @@ ROOT_STANDARD_LIBRARY_PACKAGE(Graf3d
     TPolyLine3D.cxx
     TPolyMarker3D.cxx
     TView3D.cxx
-    X3DBuffer.c
   DEPENDENCIES
     Gpad
     Graf
     Hist
     MathCore
+  LIBRARIES
+    x3d
 )
diff --git a/graf3d/g3d/inc/X3DBuffer.h b/graf3d/g3d/inc/X3DBuffer.h
index 9b6b168e2e2b4..3fc4e4bbc9837 100644
--- a/graf3d/g3d/inc/X3DBuffer.h
+++ b/graf3d/g3d/inc/X3DBuffer.h
@@ -1,42 +1 @@
-/* @(#)root/g3d:$Id$ */
-/* Author: Nenad Buncic   13/12/95*/
-
-/*************************************************************************
- * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
- * All rights reserved.                                                  *
- *                                                                       *
- * For the licensing terms see $ROOTSYS/LICENSE.                         *
- * For the list of contributors see $ROOTSYS/README/CREDITS.             *
- *************************************************************************/
-
-#ifndef ROOT_X3DBuffer
-#define ROOT_X3DBuffer
-
-typedef struct _x3d_data_ {
-   int  numPoints;
-   int  numSegs;
-   int  numPolys;
-   float *points; /* x0, y0, z0, x1, y1, z1, ..... ..... ....    */
-   int *segs;     /* c0, p0, q0, c1, p1, q1, ..... ..... ....    */
-   int *polys;    /* c0, n0, s0, s1, ... sn, c1, n1, s0, ... sn  */
-} X3DBuffer;
-
-typedef struct _x3d_sizeof_ {
-   int  numPoints;
-   int  numSegs;
-   int  numPolys;
-} Size3D;
-
-#ifdef __cplusplus
-extern "C" int AllocateX3DBuffer ();
-extern "C" void FillX3DBuffer (X3DBuffer *buff);
-extern "C" Size3D* gFuncSize3D();
-#else
-extern int AllocateX3DBuffer ();
-extern void FillX3DBuffer (X3DBuffer *buff);
-extern Size3D* gFuncSize3D();
-#endif
-
-#define gSize3D (*gFuncSize3D())
-
-#endif
+#include "../../../builtins/x3d/X3DBuffer.h" // for backward compatibility
\ No newline at end of file
diff --git a/graf3d/x3d/CMakeLists.txt b/graf3d/x3d/CMakeLists.txt
index f48ee049ffe96..6f5a49f42f915 100644
--- a/graf3d/x3d/CMakeLists.txt
+++ b/graf3d/x3d/CMakeLists.txt
@@ -5,7 +5,7 @@
 # For the list of contributors see $ROOTSYS/README/CREDITS.
 
 ############################################################################
-# CMakeLists.txt file for building ROOT graf3d/x3d package
+# CMakeLists.txt file for building ROOT graf3d/x3d C++ package
 ############################################################################
 
 ROOT_STANDARD_LIBRARY_PACKAGE(X3d
@@ -15,17 +15,12 @@ ROOT_STANDARD_LIBRARY_PACKAGE(X3d
   SOURCES
     src/TViewerX3D.cxx
     src/TX3DFrame.cxx
-    ../../builtins/x3d/x3d.c
   LIBRARIES
     ${X11_LIBRARIES}
+    x3d
   DEPENDENCIES
     Graf3d
     Gui
 )
 
-# This ROOT package depends on a hard-coded builtin C library (x3d) that was forked in 1993 and slightly adapted for ROOT. See
-# https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/x3d/inc/x3d.h
-# https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/x3d/src/x3d.c
-# vs http://hpux.connect.org.uk/hppd/hpux/X11/Viewers/x3d-2.2/ download source and rename from .tar.gz to just .tar
-
-target_include_directories(X3d PRIVATE ${X11_INCLUDE_DIR} src/ ../../builtins/x3d/) # src for src/X3DDefs.h, ../../builtins/x3d/ for x3d.h
+target_include_directories(X3d PRIVATE ${X11_INCLUDE_DIR})