diff --git a/sci-libs/Mutationpp/Mutationpp-1.0.5-r1.ebuild b/sci-libs/Mutationpp/Mutationpp-1.0.5-r1.ebuild
index ebe208161f..35030a8abd 100644
--- a/sci-libs/Mutationpp/Mutationpp-1.0.5-r1.ebuild
+++ b/sci-libs/Mutationpp/Mutationpp-1.0.5-r1.ebuild
@@ -43,7 +43,10 @@ BDEPEND="
 
 REQUIRED_USE="${PYTHON_REQUIRED_USE}"
 DOCS=( {README,CHANGELOG}.md docs )
-PATCHES=( "${FILESDIR}/${P}-system-libs.patch" )
+PATCHES=(
+	"${FILESDIR}/${P}-system-libs.patch"
+	"${FILESDIR}/${P}-respect-flags.patch"
+)
 
 distutils_enable_tests pytest
 
diff --git a/sci-libs/Mutationpp/files/Mutationpp-1.0.5-respect-flags.patch b/sci-libs/Mutationpp/files/Mutationpp-1.0.5-respect-flags.patch
new file mode 100644
index 0000000000..2f629ab546
--- /dev/null
+++ b/sci-libs/Mutationpp/files/Mutationpp-1.0.5-respect-flags.patch
@@ -0,0 +1,26 @@
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -131,7 +131,7 @@
+ 
+ if (CMAKE_COMPILER_IS_GNUCXX)
+     #set (CMAKE_CXX_FLAGS "-Wall -Wextra -Wno-unused-parameter -Wold-style-cast")
+-    set (CMAKE_CXX_FLAGS "-g")
++    set (CMAKE_CXX_FLAGS "-g ${CMAKE_CXX_FLAGS}")
+ endif ()
+ 
+ if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+@@ -152,13 +152,11 @@
+ 
+     if (Fortran_COMPILER_NAME STREQUAL "gfortran")
+         # gfortran
+-        set (CMAKE_Fortran_FLAGS         "-fdefault-real-8")
+-        set (CMAKE_Fortran_FLAGS_RELEASE "-O3")
++        set (CMAKE_Fortran_FLAGS         "-fdefault-real-8 ${CMAKE_Fortran_FLAGS}")
+         set (CMAKE_Fortran_FLAGS_DEBUG   "-g")
+     elseif (Fortran_COMPILER_NAME STREQUAL "ifort")
+         # ifort (untested)
+         set (CMAKE_Fortran_FLAGS         "-r8")
+-        set (CMAKE_Fortran_FLAGS_RELEASE "-O3")
+         set (CMAKE_Fortran_FLAGS_DEBUG   "-g -traceback -fpe0 -check all")
+     endif()
+ endif()