diff --git a/debian/patches/no-z3.patch b/debian/patches/no-z3.patch
new file mode 100644
index 00000000..8ebfd93a
--- /dev/null
+++ b/debian/patches/no-z3.patch
@@ -0,0 +1,47 @@
+Description:
+ Disable z3 to avoid pulling ocaml into main.
+ For some reason the cmake option LLVM_ENABLE_Z3_SOLVER was not taken into account
+Author: Gianfranco Costamagna <locutusofborg@debian.org>
+
+Last-Update: 2019-11-26
+
+Index: llvm-toolchain-9-9.0.0/llvm/CMakeLists.txt
+===================================================================
+--- llvm-toolchain-9-9.0.0.orig/llvm/CMakeLists.txt
++++ llvm-toolchain-9-9.0.0/llvm/CMakeLists.txt
+@@ -340,24 +340,22 @@
+ 
+ set(LLVM_Z3_INSTALL_DIR "" CACHE STRING "Install directory of the Z3 solver.")
+ 
+-find_package(Z3 4.7.1)
+-
+-if (LLVM_Z3_INSTALL_DIR)
+-  if (NOT Z3_FOUND)
+-    message(FATAL_ERROR "Z3 >= 4.7.1 has not been found in LLVM_Z3_INSTALL_DIR: ${LLVM_Z3_INSTALL_DIR}.")
+-  endif()
+-endif()
+-
+-set(LLVM_ENABLE_Z3_SOLVER_DEFAULT "${Z3_FOUND}")
+-
+ option(LLVM_ENABLE_Z3_SOLVER
+   "Enable Support for the Z3 constraint solver in LLVM."
+-  ${LLVM_ENABLE_Z3_SOLVER_DEFAULT}
++  ON
+ )
+ 
+ if (LLVM_ENABLE_Z3_SOLVER)
+-  if (NOT Z3_FOUND)
+-    message(FATAL_ERROR "LLVM_ENABLE_Z3_SOLVER cannot be enabled when Z3 is not available.")
++  find_package(Z3 4.7.1)
++
++  if (LLVM_Z3_INSTALL_DIR)
++    if (NOT Z3_FOUND)
++      message(FATAL_ERROR "Z3 >= 4.7.1 has not been found in LLVM_Z3_INSTALL_DIR: ${LLVM_Z3_INSTALL_DIR}.")
++    endif()
++  else()
++    if (NOT Z3_FOUND)
++      message(FATAL_ERROR "LLVM_ENABLE_Z3_SOLVER cannot be enabled when Z3 is not available.")
++    endif()
+   endif()
+ 
+   set(LLVM_WITH_Z3 1)
diff --git a/debian/patches/series b/debian/patches/series
index 14289090..8561d532 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -133,3 +133,4 @@ clang-riscv64-rv64gc.diff
 D67877.patch
 disable-lit-cpuid-install.diff
 disable-fuzzer-compiler-rt.diff
+no-z3.patch
diff --git a/debian/rules b/debian/rules
index b648e54f..38aa563f 100755
--- a/debian/rules
+++ b/debian/rules
@@ -70,11 +70,13 @@ ifeq ($(shell dpkg --compare-versions $(shell dpkg-query -W -f '$${Version}' g++
 	GCC_VERSION := 4.9
 endif
 
-Z3_FLAG=
+Z3_FLAG = -DLLVM_ENABLE_Z3_SOLVER=OFF
 ifeq ($(shell dpkg --compare-versions $(shell dpkg-query -W -f '$${Version}' libz3-dev) gt 4.7.0; echo $$?),0)
-# Too old version of gcc. Force 4.9
+# no ocaml support in main for Ubuntu
+ifneq ($(shell dpkg-vendor --derives-from Ubuntu && echo yes),yes)
 	Z3_FLAG = -DLLVM_ENABLE_Z3_SOLVER=ON
 endif
+endif
 
 FORCE_NOT_GCC_9_DISTRO := eoan focal bullseye sid
 ifneq (,$(filter $(DISTRO),$(FORCE_NOT_GCC_9_DISTRO)))