diff --git a/build-aux/m4/bitcoin_qt.m4 b/build-aux/m4/bitcoin_qt.m4
index 89f3e188ee..25a5217345 100644
--- a/build-aux/m4/bitcoin_qt.m4
+++ b/build-aux/m4/bitcoin_qt.m4
@@ -116,8 +116,8 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
   BITCOIN_QT_CHECK([
   TEMP_CPPFLAGS=$CPPFLAGS
   TEMP_CXXFLAGS=$CXXFLAGS
-  CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
-  CXXFLAGS="$PIC_FLAGS $CXXFLAGS"
+  CPPFLAGS="$QT_INCLUDES $CORE_CPPFLAGS $CPPFLAGS"
+  CXXFLAGS="$PIC_FLAGS $CORE_CXXFLAGS $CXXFLAGS"
   _BITCOIN_QT_IS_STATIC
   if test "x$bitcoin_cv_static_qt" = xyes; then
     _BITCOIN_QT_CHECK_STATIC_LIBS
@@ -177,8 +177,8 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     AC_MSG_CHECKING(whether -fPIE can be used with this Qt config)
     TEMP_CPPFLAGS=$CPPFLAGS
     TEMP_CXXFLAGS=$CXXFLAGS
-    CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
-    CXXFLAGS="$PIE_FLAGS $CXXFLAGS"
+    CPPFLAGS="$QT_INCLUDES $CORE_CPPFLAGS $CPPFLAGS"
+    CXXFLAGS="$PIE_FLAGS $CORE_CXXFLAGS $CXXFLAGS"
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
         #include <QtCore/qconfig.h>
         #ifndef QT_VERSION
@@ -200,7 +200,7 @@ AC_DEFUN([BITCOIN_QT_CONFIGURE],[
     BITCOIN_QT_CHECK([
     AC_MSG_CHECKING(whether -fPIC is needed with this Qt config)
     TEMP_CPPFLAGS=$CPPFLAGS
-    CPPFLAGS="$QT_INCLUDES $CPPFLAGS"
+    CPPFLAGS="$QT_INCLUDES $CORE_CPPFLAGS $CPPFLAGS"
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
         #include <QtCore/qconfig.h>
         #ifndef QT_VERSION
diff --git a/configure.ac b/configure.ac
index 7ad8aa107b..b852a2e729 100644
--- a/configure.ac
+++ b/configure.ac
@@ -372,7 +372,9 @@ case $host in
 esac
 
 if test "x$enable_debug" = xyes; then
-  dnl Clear default -g -O2 flags
+  dnl If debugging is enabled, and the user hasn't overriden CXXFLAGS, clear
+  dnl them, to prevent autoconfs "-g -O2" being added. Otherwise we'd end up
+  dnl with "-O0 -g3 -g -O2".
   if test "x$CXXFLAGS_overridden" = xno; then
 	CXXFLAGS=""
   fi
@@ -532,7 +534,7 @@ if test "x$CXXFLAGS_overridden" = "xno"; then
 fi
 
 dnl Don't allow extended (non-ASCII) symbols in identifiers. This is easier for code review.
-AX_CHECK_COMPILE_FLAG([-fno-extended-identifiers],[[CXXFLAGS="$CXXFLAGS -fno-extended-identifiers"]],,[[$CXXFLAG_WERROR]])
+AX_CHECK_COMPILE_FLAG([-fno-extended-identifiers],[[CORE_CXXFLAGS="$CORE_CXXFLAGS -fno-extended-identifiers"]],,[[$CXXFLAG_WERROR]])
 
 enable_arm_crc=no
 enable_arm_shani=no
@@ -683,7 +685,7 @@ CXXFLAGS="$TEMP_CXXFLAGS"
 
 fi
 
-CPPFLAGS="$CPPFLAGS -DHAVE_BUILD_INFO -DGSL_NO_IOSTREAMS"
+CORE_CPPFLAGS="$CORE_CPPFLAGS -DHAVE_BUILD_INFO -DGSL_NO_IOSTREAMS"
 
 AC_ARG_WITH([utils],
   [AS_HELP_STRING([--with-utils],
@@ -755,7 +757,7 @@ case $host in
        AC_MSG_ERROR("windres not found")
      fi
 
-     CPPFLAGS="$CPPFLAGS -D_MT -DWIN32 -D_WINDOWS -D_WIN32_WINNT=0x0601 -D_WIN32_IE=0x0501 -DWIN32_LEAN_AND_MEAN"
+     CORE_CPPFLAGS="$CORE_CPPFLAGS -D_MT -DWIN32 -D_WINDOWS -D_WIN32_WINNT=0x0601 -D_WIN32_IE=0x0501 -DWIN32_LEAN_AND_MEAN"
 
      dnl libtool insists upon adding -nostdlib and a list of objects/libs to link against.
      dnl That breaks our ability to build dll's with static libgcc/libstdc++/libssp. Override
@@ -766,14 +768,14 @@ case $host in
      postdeps_CXX=
 
      dnl We require Windows 7 (NT 6.1) or later
-     AX_CHECK_LINK_FLAG([[-Wl,--major-subsystem-version -Wl,6 -Wl,--minor-subsystem-version -Wl,1]],[LDFLAGS="$LDFLAGS -Wl,--major-subsystem-version -Wl,6 -Wl,--minor-subsystem-version -Wl,1"],,[[$LDFLAG_WERROR]])
+     AX_CHECK_LINK_FLAG([[-Wl,--major-subsystem-version -Wl,6 -Wl,--minor-subsystem-version -Wl,1]],[CORE_LDFLAGS="$CORE_LDFLAGS -Wl,--major-subsystem-version -Wl,6 -Wl,--minor-subsystem-version -Wl,1"],,[[$LDFLAG_WERROR]])
      ;;
   *darwin*)
      TARGET_OS=darwin
      if  test x$cross_compiling != xyes; then
        BUILD_OS=darwin
 
-       AX_CHECK_LINK_FLAG([[-Wl,-headerpad_max_install_names]], [LDFLAGS="$LDFLAGS -Wl,-headerpad_max_install_names"],, [[$LDFLAG_WERROR]])
+       AX_CHECK_LINK_FLAG([[-Wl,-headerpad_max_install_names]], [CORE_LDFLAGS="$CORE_LDFLAGS -Wl,-headerpad_max_install_names"],, [[$LDFLAG_WERROR]])
 
        AC_CHECK_PROG([BREW],brew, brew)
        if test x$BREW = xbrew; then
@@ -800,8 +802,8 @@ case $host in
 
          gmp_prefix=$($BREW --prefix gmp 2>/dev/null)
          if test x$gmp_prefix != x; then
-           CPPFLAGS="$CPPFLAGS -I$gmp_prefix/include"
-           LDFLAGS="$LDFLAGS -L$gmp_prefix/lib"
+           CORE_CPPFLAGS="$CORE_CPPFLAGS -I$gmp_prefix/include"
+           CORE_LDFLAGS="$CORE_LDFLAGS -L$gmp_prefix/lib"
          fi
 
          case $host in
@@ -813,20 +815,20 @@ case $host in
              if test "x$use_upnp" != xno && $BREW list --versions miniupnpc >/dev/null; then
                miniupnpc_prefix=$($BREW --prefix miniupnpc 2>/dev/null)
                if test "x$suppress_external_warnings" != xno; then
-                 CPPFLAGS="$CPPFLAGS -isystem $miniupnpc_prefix/include"
+                 CORE_CPPFLAGS="$CORE_CPPFLAGS -isystem $miniupnpc_prefix/include"
                else
-                 CPPFLAGS="$CPPFLAGS -I$miniupnpc_prefix/include"
+                 CORE_CPPFLAGS="$CORE_CPPFLAGS -I$miniupnpc_prefix/include"
                fi
-               LDFLAGS="$LDFLAGS -L$miniupnpc_prefix/lib"
+               CORE_LDFLAGS="$CORE_LDFLAGS -L$miniupnpc_prefix/lib"
              fi
              if test "x$use_natpmp" != xno && $BREW list --versions libnatpmp >/dev/null; then
                libnatpmp_prefix=$($BREW --prefix libnatpmp 2>/dev/null)
                if test "x$suppress_external_warnings" != xno; then
-                 CPPFLAGS="$CPPFLAGS -isystem $libnatpmp_prefix/include"
+                 CORE_CPPFLAGS="$CORE_CPPFLAGS -isystem $libnatpmp_prefix/include"
                else
-                 CPPFLAGS="$CPPFLAGS -I$libnatpmp_prefix/include"
+                 CORE_CPPFLAGS="$CORE_CPPFLAGS -I$libnatpmp_prefix/include"
                fi
-               LDFLAGS="$LDFLAGS -L$libnatpmp_prefix/lib"
+               CORE_LDFLAGS="$CORE_LDFLAGS -L$libnatpmp_prefix/lib"
              fi
              ;;
          esac
@@ -849,7 +851,7 @@ case $host in
        esac
      fi
 
-     CPPFLAGS="$CPPFLAGS -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0"
+     CORE_CPPFLAGS="$CORE_CPPFLAGS -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0"
      OBJCXXFLAGS="$CXXFLAGS"
      ;;
    *android*)
@@ -912,11 +914,17 @@ if test x$use_lcov = xyes; then
   AC_SUBST(COV_TOOL_WRAPPER, "cov_tool_wrapper.sh")
   LCOV="$LCOV --gcov-tool $(pwd)/$COV_TOOL_WRAPPER"
 
-  AX_CHECK_LINK_FLAG([[--coverage]], [LDFLAGS="$LDFLAGS --coverage"],
+  AX_CHECK_LINK_FLAG([[--coverage]], [CORE_LDFLAGS="$CORE_LDFLAGS --coverage"],
     [AC_MSG_ERROR("lcov testing requested but --coverage linker flag does not work")])
-  AX_CHECK_COMPILE_FLAG([--coverage],[CXXFLAGS="$CXXFLAGS --coverage"],
+  AX_CHECK_COMPILE_FLAG([--coverage],[CORE_CXXFLAGS="$CORE_CXXFLAGS --coverage"],
     [AC_MSG_ERROR("lcov testing requested but --coverage flag does not work")])
-  CXXFLAGS="$CXXFLAGS -Og"
+  dnl If coverage is enabled, and the user hasn't overriden CXXFLAGS, clear
+  dnl them, to prevent autoconfs "-g -O2" being added. Otherwise we'd end up
+  dnl with "--coverage -Og -O0 -g -O2".
+  if test "$CXXFLAGS_overridden" = "no"; then
+  CXXFLAGS=""
+  fi
+  CORE_CXXFLAGS="$CORE_CXXFLAGS -Og -O0"
 fi
 
 if test x$use_lcov_branch != xno; then
@@ -942,13 +950,13 @@ AC_FUNC_STRERROR_R
 if test x$ac_cv_sys_file_offset_bits != x &&
    test x$ac_cv_sys_file_offset_bits != xno &&
    test x$ac_cv_sys_file_offset_bits != xunknown; then
-  CPPFLAGS="$CPPFLAGS -D_FILE_OFFSET_BITS=$ac_cv_sys_file_offset_bits"
+  CORE_CPPFLAGS="$CORE_CPPFLAGS -D_FILE_OFFSET_BITS=$ac_cv_sys_file_offset_bits"
 fi
 
 if test x$ac_cv_sys_large_files != x &&
    test x$ac_cv_sys_large_files != xno &&
    test x$ac_cv_sys_large_files != xunknown; then
-  CPPFLAGS="$CPPFLAGS -D_LARGE_FILES=$ac_cv_sys_large_files"
+  CORE_CPPFLAGS="$CORE_CPPFLAGS -D_LARGE_FILES=$ac_cv_sys_large_files"
 fi
 
 if test "x$enable_gprof" = xyes; then
@@ -1037,8 +1045,8 @@ dnl These flags are specific to ld64, and may cause issues with other linkers.
 dnl For example: GNU ld will interpret -dead_strip as -de and then try and use
 dnl "ad_strip" as the symbol for the entry point.
 if test x$TARGET_OS = xdarwin; then
-  AX_CHECK_LINK_FLAG([[-Wl,-dead_strip]], [LDFLAGS="$LDFLAGS -Wl,-dead_strip"],, [[$LDFLAG_WERROR]])
-  AX_CHECK_LINK_FLAG([[-Wl,-dead_strip_dylibs]], [LDFLAGS="$LDFLAGS -Wl,-dead_strip_dylibs"],, [[$LDFLAG_WERROR]])
+  AX_CHECK_LINK_FLAG([[-Wl,-dead_strip]], [CORE_LDFLAGS="$CORE_LDFLAGS -Wl,-dead_strip"],, [[$LDFLAG_WERROR]])
+  AX_CHECK_LINK_FLAG([[-Wl,-dead_strip_dylibs]], [CORE_LDFLAGS="$CORE_LDFLAGS -Wl,-dead_strip_dylibs"],, [[$LDFLAG_WERROR]])
   AX_CHECK_LINK_FLAG([[-Wl,-fixup_chains]], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-fixup_chains"], [], [[$LDFLAG_WERROR]])
 fi
 
@@ -1360,7 +1368,7 @@ if test "x$enable_fuzz" = "xyes"; then
     [[-fsanitize=$use_sanitizers]],
     [AC_MSG_RESULT([no])],
     [AC_MSG_RESULT([yes])
-     CPPFLAGS="$CPPFLAGS -DPROVIDE_FUZZ_MAIN_FUNCTION"],
+     CORE_CPPFLAGS="$CORE_CPPFLAGS -DPROVIDE_FUZZ_MAIN_FUNCTION"],
     [],
     [AC_LANG_PROGRAM([[
       #include <cstdint>
@@ -1384,7 +1392,7 @@ else
       QT_TEST_INCLUDES=SUPPRESS_WARNINGS($QT_TEST_INCLUDES)
     fi
 
-    CPPFLAGS="$CPPFLAGS -DPROVIDE_FUZZ_MAIN_FUNCTION"
+    CORE_CPPFLAGS="$CORE_CPPFLAGS -DPROVIDE_FUZZ_MAIN_FUNCTION"
 fi
 
 if test x$enable_wallet != xno; then
@@ -1517,7 +1525,7 @@ fi
 
 dnl Check for reduced exports
 if test x$use_reduce_exports = xyes; then
-    AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[CXXFLAGS="$CXXFLAGS -fvisibility=hidden"],
+    AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],[CORE_CXXFLAGS="$CORE_CXXFLAGS -fvisibility=hidden"],
     [AC_MSG_ERROR([Cannot set hidden symbol visibility. Use --disable-reduce-exports.])],[[$CXXFLAG_WERROR]])
     AX_CHECK_LINK_FLAG([[-Wl,--exclude-libs,ALL]],[RELDFLAGS="-Wl,--exclude-libs,ALL"],,[[$LDFLAG_WERROR]])
     AX_CHECK_LINK_FLAG([-Wl,-no_exported_symbols], [LIBTOOL_APP_LDFLAGS="$LIBTOOL_APP_LDFLAGS -Wl,-no_exported_symbols"], [], [$LDFLAG_WERROR])
@@ -1869,6 +1877,9 @@ AC_SUBST(BITCOIN_MP_NODE_NAME)
 AC_SUBST(BITCOIN_MP_GUI_NAME)
 
 AC_SUBST(RELDFLAGS)
+AC_SUBST(CORE_LDFLAGS)
+AC_SUBST(CORE_CPPFLAGS)
+AC_SUBST(CORE_CXXFLAGS)
 AC_SUBST(DEBUG_CPPFLAGS)
 AC_SUBST(WARN_CXXFLAGS)
 AC_SUBST(NOWARN_CXXFLAGS)
@@ -1995,9 +2006,9 @@ echo "  build os            = $build_os"
 echo
 echo "  CC                  = $CC"
 echo "  CFLAGS              = $PTHREAD_CFLAGS $CFLAGS"
-echo "  CPPFLAGS            = $DEBUG_CPPFLAGS $HARDENED_CPPFLAGS $CPPFLAGS"
+echo "  CPPFLAGS            = $DEBUG_CPPFLAGS $HARDENED_CPPFLAGS $CORE_CPPFLAGS $CPPFLAGS"
 echo "  CXX                 = $CXX"
-echo "  CXXFLAGS            = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CXXFLAGS"
-echo "  LDFLAGS             = $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $LDFLAGS"
+echo "  CXXFLAGS            = $DEBUG_CXXFLAGS $HARDENED_CXXFLAGS $WARN_CXXFLAGS $NOWARN_CXXFLAGS $ERROR_CXXFLAGS $GPROF_CXXFLAGS $CORE_CXXFLAGS $CXXFLAGS"
+echo "  LDFLAGS             = $PTHREAD_LIBS $HARDENED_LDFLAGS $GPROF_LDFLAGS $CORE_LDFLAGS $LDFLAGS"
 echo "  ARFLAGS             = $ARFLAGS"
 echo
diff --git a/src/Makefile.am b/src/Makefile.am
index 7dfa2c6073..2061684a4b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -9,9 +9,9 @@ print-%: FORCE
 
 DIST_SUBDIRS = secp256k1
 
-AM_LDFLAGS = $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS) $(GPROF_LDFLAGS) $(SANITIZER_LDFLAGS)
-AM_CXXFLAGS = $(DEBUG_CXXFLAGS) $(HARDENED_CXXFLAGS) $(WARN_CXXFLAGS) $(NOWARN_CXXFLAGS) $(ERROR_CXXFLAGS) $(GPROF_CXXFLAGS) $(SANITIZER_CXXFLAGS)
-AM_CPPFLAGS = $(DEBUG_CPPFLAGS) $(HARDENED_CPPFLAGS)
+AM_LDFLAGS = $(LIBTOOL_LDFLAGS) $(HARDENED_LDFLAGS) $(GPROF_LDFLAGS) $(SANITIZER_LDFLAGS) $(CORE_LDFLAGS)
+AM_CXXFLAGS = $(DEBUG_CXXFLAGS) $(HARDENED_CXXFLAGS) $(WARN_CXXFLAGS) $(NOWARN_CXXFLAGS) $(ERROR_CXXFLAGS) $(GPROF_CXXFLAGS) $(SANITIZER_CXXFLAGS) $(CORE_CXXFLAGS)
+AM_CPPFLAGS = $(DEBUG_CPPFLAGS) $(HARDENED_CPPFLAGS) $(CORE_CPPFLAGS)
 AM_LIBTOOLFLAGS = --preserve-dup-deps
 PTHREAD_FLAGS = $(PTHREAD_CFLAGS) $(PTHREAD_LIBS)
 EXTRA_LIBRARIES =