diff --git a/CMakeLists.txt b/CMakeLists.txt
index 23f6b90b10453..20ae8a46c58cc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -393,6 +393,7 @@ install(FILES ${CMAKE_BINARY_DIR}/etc/gitinfo.txt DESTINATION ${CMAKE_INSTALL_SY
 #---Recurse into the given subdirectories.  This does not actually cause another cmake executable
 #  to run. The same process will walk through the project's entire directory structure.
 add_subdirectory (core)
+add_subdirectory (builtins/zip) # hard coded builtin for core/zip
 add_subdirectory (math)
 add_subdirectory (hist)
 add_subdirectory (tree)
diff --git a/core/zip/src/Bits.c b/builtins/zip/Bits.c
similarity index 100%
rename from core/zip/src/Bits.c
rename to builtins/zip/Bits.c
diff --git a/core/zip/src/Bits.h b/builtins/zip/Bits.h
similarity index 100%
rename from core/zip/src/Bits.h
rename to builtins/zip/Bits.h
diff --git a/builtins/zip/CMakeLists.txt b/builtins/zip/CMakeLists.txt
new file mode 100644
index 0000000000000..c01f3c2159689
--- /dev/null
+++ b/builtins/zip/CMakeLists.txt
@@ -0,0 +1,15 @@
+# Copyright (C) 1995-2026, Rene Brun and Fons Rademakers.
+# All rights reserved.
+#
+# For the licensing terms see $ROOTSYS/LICENSE.
+# For the list of contributors see $ROOTSYS/README/CREDITS.
+
+target_sources(Core PRIVATE
+  Bits.h # was renamed from Bits.c at https://github.com/root-project/root/commit/3b2f05c8ddf1001cc8eb05ad60b07b10af6ac293#diff-ff111e76990c56e7019ed0d837f1f615e280dc679ed393200c4f75b61094c5b7 and later split back to Bits.c in https://github.com/root-project/root/commit/25d5805abac4d408554e99aec6e49b8a671a2d96
+  Tailor.h # forked from 1993: zip 2.0 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/inc/Tailor.h vs https://github.com/pmqs/Info-ZIP-Family-Tree-for-Zip/blob/d25ed515bc56fae136b635d764ce8b363041aef5/tailor.h)
+  ZIP.h  # forked from 1993: zip 2.0 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/inc/ZIP.h vs https://github.com/pmqs/Info-ZIP-Family-Tree-for-Zip/blob/d25ed515bc56fae136b635d764ce8b363041aef5/zip.h)
+  Bits.c # forked from 1993: zip 2.0 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/src/Bits.c vs https://github.com/pmqs/Info-ZIP-Family-Tree-for-Zip/blob/d25ed515bc56fae136b635d764ce8b363041aef5/bits.c)
+  ZDeflate.c # forked from 1993: zip 2.0 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/src/Deflate.c vs https://github.com/pmqs/Info-ZIP-Family-Tree-for-Zip/blob/d25ed515bc56fae136b635d764ce8b363041aef5/deflate.c)
+  ZInflate.c # forked from 1994: version c14o / unzip-5.12 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/src/Inflate.c vs https://github.com/freebsd/freebsd-src/commit/37c32e9f3a0dc8ba9d0b7cd06742502dcba1b457 or https://stuff.mit.edu/afs/sipb.mit.edu/project/sipbsrc/i386_nbsd1/unzip-5.12/inflate.c)
+  ZTrees.c # forked from 1993: zip 2.0 (https://github.com/root-project/root/blob/852600061bcacd9b255d44f6312c96b6b1e00a2d/zip/src/Trees.c vs https://github.com/pmqs/Info-ZIP-Family-Tree-for-Zip/blob/d25ed515bc56fae136b635d764ce8b363041aef5/trees.c)
+)
diff --git a/core/zip/src/Tailor.h b/builtins/zip/Tailor.h
similarity index 100%
rename from core/zip/src/Tailor.h
rename to builtins/zip/Tailor.h
diff --git a/core/zip/src/ZDeflate.c b/builtins/zip/ZDeflate.c
similarity index 100%
rename from core/zip/src/ZDeflate.c
rename to builtins/zip/ZDeflate.c
diff --git a/core/zip/src/ZIP.h b/builtins/zip/ZIP.h
similarity index 100%
rename from core/zip/src/ZIP.h
rename to builtins/zip/ZIP.h
diff --git a/core/zip/src/ZInflate.c b/builtins/zip/ZInflate.c
similarity index 100%
rename from core/zip/src/ZInflate.c
rename to builtins/zip/ZInflate.c
diff --git a/core/zip/src/ZTrees.c b/builtins/zip/ZTrees.c
similarity index 100%
rename from core/zip/src/ZTrees.c
rename to builtins/zip/ZTrees.c
diff --git a/core/zip/CMakeLists.txt b/core/zip/CMakeLists.txt
index 72d1bfb756dd8..e800fbbf4d6a3 100644
--- a/core/zip/CMakeLists.txt
+++ b/core/zip/CMakeLists.txt
@@ -7,15 +7,12 @@
 find_package(ZLIB REQUIRED)
 
 target_sources(Core PRIVATE
-  src/Bits.c
-  src/ZDeflate.c
-  src/ZTrees.c
-  src/ZInflate.c
   src/Compression.cxx
   src/RZip.cxx
 )
 
 target_link_libraries(Core PRIVATE ZLIB::ZLIB)
+target_include_directories(Core PRIVATE ../../builtins/zip)
 
 target_include_directories(Core PUBLIC
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/inc>