diff --git a/configure.ac b/configure.ac
--- a/configure.ac
+++ b/configure.ac
@@ -295,6 +295,7 @@
   AX_CHECK_COMPILE_FLAG([-Wshadow],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wshadow"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wmissing-braces],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wmissing-braces"],,[[$CXXFLAG_WERROR]])
   AX_CHECK_COMPILE_FLAG([-Wrange-loop-analysis],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wrange-loop-analysis"],,[[$CXXFLAG_WERROR]])
+  AX_CHECK_COMPILE_FLAG([-Wredundant-decls],[WARN_CXXFLAGS="$WARN_CXXFLAGS -Wredundant-decls"],,[[$CXXFLAG_WERROR]])
 
   ## Some compilers (gcc) ignore unknown -Wno-* options, but warn about all
   ## unknown options if any other warning is produced. Test the -Wfoo case, and
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -137,6 +137,7 @@
 	-Wthread-safety-analysis
 	-Wshadow
 	-Wrange-loop-analysis
+	-Wredundant-decls
 )
 
 option(EXTRA_WARNINGS "Enable extra warnings" OFF)