diff --git a/toolchain/Config.in b/toolchain/Config.in
index 7b0a0aaeee..e89cdf6345 100644
--- a/toolchain/Config.in
+++ b/toolchain/Config.in
@@ -26,7 +26,14 @@ config LARGEFILE
 	depends on !cris
 	default y
 	help
-	    Enable large file (files > 2 GB) support
+		Enable large file (files > 2 GB) support
+
+config C99_MATH
+	bool
+	prompt "Enable full C99 math support?" if TOOLCHAINOPTS
+	default n
+	help
+		Enable if you need full C99 math in libm
 
 config SOFT_FLOAT
 	bool
diff --git a/toolchain/uClibc/Makefile b/toolchain/uClibc/Makefile
index b640405ddc..7fdba8aded 100644
--- a/toolchain/uClibc/Makefile
+++ b/toolchain/uClibc/Makefile
@@ -51,6 +51,9 @@ endif
 	$(SED) 's,.*UCLIBC_HAS_WCHAR.*,UCLIBC_HAS_WCHAR=y,g' $(PKG_BUILD_DIR)/.config
 ifeq ($(CONFIG_SOFT_FLOAT),y)
 	$(SED) 's,.*HAS_FPU.*,HAS_FPU=n\nUCLIBC_HAS_FLOATS=y\nUCLIBC_HAS_SOFT_FLOAT=y,g' $(PKG_BUILD_DIR)/.config
+endif
+ifeq ($(CONFIG_C99_MATH),y)
+	$(SED) 's,.*DO_C99_MATH.*,DO_C99_MATH=y,g' $(PKG_BUILD_DIR)/.config
 endif
 	mkdir -p $(TOOLCHAIN_BUILD_DIR)/uClibc_dev/usr/include
 	mkdir -p $(TOOLCHAIN_BUILD_DIR)/uClibc_dev/usr/lib