diff --git a/sys-libs/llvm-libunwind/llvm-libunwind-16.0.6.ebuild b/sys-libs/llvm-libunwind/llvm-libunwind-16.0.6-r1.ebuild
similarity index 88%
rename from sys-libs/llvm-libunwind/llvm-libunwind-16.0.6.ebuild
rename to sys-libs/llvm-libunwind/llvm-libunwind-16.0.6-r1.ebuild
index 9d53bcd51939d..18d5066e295f6 100644
--- a/sys-libs/llvm-libunwind/llvm-libunwind-16.0.6.ebuild
+++ b/sys-libs/llvm-libunwind/llvm-libunwind-16.0.6-r1.ebuild
@@ -67,6 +67,15 @@ multilib_src_configure() {
 	local use_compiler_rt=OFF
 	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
 
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
 	local mycmakeargs=(
 		-DCMAKE_CXX_COMPILER_TARGET="${CHOST}"
 		-DPython3_EXECUTABLE="${PYTHON}"
diff --git a/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0.9999.ebuild b/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0.9999.ebuild
index 43f8868fc308a..94ec81df14521 100644
--- a/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0.9999.ebuild
+++ b/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0.9999.ebuild
@@ -67,6 +67,15 @@ multilib_src_configure() {
 	local use_compiler_rt=OFF
 	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
 
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
 	local mycmakeargs=(
 		-DCMAKE_CXX_COMPILER_TARGET="${CHOST}"
 		-DPython3_EXECUTABLE="${PYTHON}"
diff --git a/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4.ebuild b/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4-r1.ebuild
similarity index 88%
rename from sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4.ebuild
rename to sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4-r1.ebuild
index 43f8868fc308a..94ec81df14521 100644
--- a/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4.ebuild
+++ b/sys-libs/llvm-libunwind/llvm-libunwind-17.0.0_rc4-r1.ebuild
@@ -67,6 +67,15 @@ multilib_src_configure() {
 	local use_compiler_rt=OFF
 	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
 
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
 	local mycmakeargs=(
 		-DCMAKE_CXX_COMPILER_TARGET="${CHOST}"
 		-DPython3_EXECUTABLE="${PYTHON}"
diff --git a/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0.9999.ebuild b/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0.9999.ebuild
index 43f8868fc308a..94ec81df14521 100644
--- a/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0.9999.ebuild
+++ b/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0.9999.ebuild
@@ -67,6 +67,15 @@ multilib_src_configure() {
 	local use_compiler_rt=OFF
 	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
 
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
 	local mycmakeargs=(
 		-DCMAKE_CXX_COMPILER_TARGET="${CHOST}"
 		-DPython3_EXECUTABLE="${PYTHON}"
diff --git a/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906.ebuild b/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906-r1.ebuild
similarity index 88%
rename from sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906.ebuild
rename to sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906-r1.ebuild
index 43f8868fc308a..94ec81df14521 100644
--- a/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906.ebuild
+++ b/sys-libs/llvm-libunwind/llvm-libunwind-18.0.0_pre20230906-r1.ebuild
@@ -67,6 +67,15 @@ multilib_src_configure() {
 	local use_compiler_rt=OFF
 	[[ $(tc-get-c-rtlib) == compiler-rt ]] && use_compiler_rt=ON
 
+	# Respect upstream build type assumptions (bug #910436) where they do:
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=ON =>
+	#       -DCMAKE_BUILD_TYPE=DEBUG  => -UNDEBUG
+	#       -DCMAKE_BUILD_TYPE!=debug => -DNDEBUG
+	# -DLIBUNWIND_ENABLE_ASSERTIONS=OFF =>
+	#       -UNDEBUG
+	# See also https://github.com/llvm/llvm-project/issues/86#issuecomment-1649668826.
+	use debug || append-cppflags -DNDEBUG
+
 	local mycmakeargs=(
 		-DCMAKE_CXX_COMPILER_TARGET="${CHOST}"
 		-DPython3_EXECUTABLE="${PYTHON}"