diff --git a/configure.ac b/configure.ac
index bdf5d3df29..35618f62ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5118,6 +5118,11 @@ then
     ENABLED_CURVE25519="yes"
 fi
 
+if test "$ENABLED_CURVE25519" = "no" && test "$ENABLED_LIGHTY" = "yes" && test "x$ENABLED_FIPS" = "xno"
+then
+    ENABLED_CURVE25519="yes"
+fi
+
 
 # ED25519
 AC_ARG_ENABLE([ed25519],
@@ -10480,6 +10485,23 @@ if test "$ENABLED_SP_MATH_ALL" = "yes" && test "$ENABLED_ASM" != "no"; then
 fi
 
 
+if test "$ENABLED_SP_ASM" = "yes" && test "$ENABLED_SP" = "yes"; then
+  case $host_cpu in
+  *x86_64* | *amd64*)
+    case $host_os in
+    *mingw* | *cygwin* | *msys*)
+      if test "$enable_sp_asm" = "yes"; then
+        AC_MSG_ERROR([--enable-sp-asm is not supported for x86_64 Windows hosts (MinGW/Cygwin). Reconfigure without --enable-sp-asm to use the C SP implementation.])
+      else
+        AC_MSG_WARN([x86_64 SP assembly is not supported for Windows hosts (MinGW/Cygwin); disabling SP assembly and using the C implementation.])
+        ENABLED_SP_ASM=no
+      fi
+      ;;
+    esac
+    ;;
+  esac
+fi
+
 if test "$ENABLED_SP_ASM" = "yes" && test "$ENABLED_SP" = "yes"; then
   if test "$ENABLED_SP_NONBLOCK" = "yes"; then
     AC_MSG_ERROR([SP non-blocking not supported with sp-asm])
@@ -12489,6 +12511,16 @@ if test "x$WOLFSSL_EXEC_PREFIX_ABS" = "xNONE"; then
 fi
 prefix=$WOLFSSL_PREFIX_ABS
 exec_prefix=$WOLFSSL_EXEC_PREFIX_ABS
+# The eval calls below expand ${prefix}/${exec_prefix} references embedded in
+# the libdir/includedir values. eval would, however, also execute any shell
+# command substitution contained in a --libdir/--includedir value (e.g.
+# --libdir='$(cmd)/lib'), running arbitrary commands during configure.
+# Reject values that contain command substitution before the eval.
+case "$libdir $includedir" in
+    *'`'* | *'$('*)
+        AC_MSG_ERROR([--libdir and --includedir must not contain shell command substitution])
+        ;;
+esac
 eval WOLFSSL_LIBDIR_ABS=\"$libdir\"
 eval WOLFSSL_INCLUDEDIR_ABS=\"$includedir\"
 AC_SUBST([WOLFSSL_PREFIX_ABS])