diff --git a/Makefile b/Makefile
index f9e65d1b2..d3d8bbc83 100644
--- a/Makefile
+++ b/Makefile
@@ -157,6 +157,7 @@ include third_party/quickjs/quickjs.mk
 include third_party/lz4cli/lz4cli.mk
 include third_party/zip/zip.mk
 include third_party/unzip/unzip.mk
+include third_party/double-conversion/double-conversion.mk
 include tool/build/lib/buildlib.mk
 include third_party/chibicc/chibicc.mk
 include third_party/chibicc/test/test.mk
diff --git a/third_party/double-conversion/double-conversion.mk b/third_party/double-conversion/double-conversion.mk
new file mode 100644
index 000000000..a19a123ef
--- /dev/null
+++ b/third_party/double-conversion/double-conversion.mk
@@ -0,0 +1,60 @@
+#-*-mode:makefile-gmake;indent-tabs-mode:t;tab-width:8;coding:utf-8-*-┐
+#───vi: set et ft=make ts=8 tw=8 fenc=utf-8 :vi───────────────────────┘
+
+PKGS += THIRD_PARTY_DOUBLECONVERSION
+
+THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS += THIRD_PARTY_DOUBLECONVERSION_A
+THIRD_PARTY_DOUBLECONVERSION = $(THIRD_PARTY_DOUBLECONVERSION_A_DEPS) $(THIRD_PARTY_DOUBLECONVERSION_A)
+THIRD_PARTY_DOUBLECONVERSION_A = o/$(MODE)/third_party/double-conversion/libdouble-conversion.a
+
+THIRD_PARTY_DOUBLECONVERSION_A_FILES := $(wildcard third_party/double-conversion/*)
+THIRD_PARTY_DOUBLECONVERSION_A_SRCS_CC = $(filter %.cc,$(THIRD_PARTY_DOUBLECONVERSION_A_FILES))
+THIRD_PARTY_DOUBLECONVERSION_A_HDRS = $(filter %.h,$(THIRD_PARTY_DOUBLECONVERSION_A_FILES))
+
+THIRD_PARTY_DOUBLECONVERSION_A_OBJS =					\
+	$(THIRD_PARTY_DOUBLECONVERSION_A_SRCS_CC:%.cc=o/$(MODE)/%.o)
+
+THIRD_PARTY_DOUBLECONVERSION_A_CHECKS =					\
+	$(THIRD_PARTY_DOUBLECONVERSION_A).pkg				\
+	$(THIRD_PARTY_DOUBLECONVERSION_A_HDRS:%=o/$(MODE)/%.okk)
+
+THIRD_PARTY_DOUBLECONVERSION_A_DIRECTDEPS =				\
+	LIBC_INTRIN						\
+	LIBC_NEXGEN32E						\
+	LIBC_MEM						\
+	LIBC_RUNTIME						\
+	LIBC_RAND						\
+	LIBC_STDIO						\
+	LIBC_FMT						\
+	LIBC_SYSV						\
+	LIBC_STR						\
+	LIBC_STUBS						\
+	LIBC_TINYMATH						\
+	THIRD_PARTY_GDTOA				\
+	THIRD_PARTY_LIBCXX
+
+THIRD_PARTY_DOUBLECONVERSION_A_DEPS :=					\
+	$(call uniq,$(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_A_DIRECTDEPS),$($(x))))
+
+$(THIRD_PARTY_DOUBLECONVERSION_A):					\
+		third_party/double-conversion/				\
+		$(THIRD_PARTY_DOUBLECONVERSION_A).pkg			\
+		$(THIRD_PARTY_DOUBLECONVERSION_A_OBJS)
+
+$(THIRD_PARTY_DOUBLECONVERSION_A).pkg:					\
+		$(THIRD_PARTY_DOUBLECONVERSION_A_OBJS)			\
+		$(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_A_DIRECTDEPS),$($(x)_A).pkg)
+
+$(THIRD_PARTY_DOUBLECONVERSION_A_OBJS):					\
+		OVERRIDE_CXXFLAGS +=				\
+			-ffunction-sections			\
+			-fdata-sections
+
+THIRD_PARTY_DOUBLECONVERSION_LIBS = $(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS),$($(x)))
+THIRD_PARTY_DOUBLECONVERSION_SRCS = $(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS),$($(x)_SRCS))
+THIRD_PARTY_DOUBLECONVERSION_HDRS = $(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS),$($(x)_HDRS))
+THIRD_PARTY_DOUBLECONVERSION_CHECKS = $(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS),$($(x)_CHECKS))
+THIRD_PARTY_DOUBLECONVERSION_OBJS = $(foreach x,$(THIRD_PARTY_DOUBLECONVERSION_ARTIFACTS),$($(x)_OBJS))
+
+.PHONY: o/$(MODE)/third_party/double-conversion
+o/$(MODE)/third_party/double-conversion: $(THIRD_PARTY_DOUBLECONVERSION_CHECKS)
diff --git a/third_party/double-conversion/string-to-double.cc b/third_party/double-conversion/string-to-double.cc
index 4a0634363..752cc0cea 100644
--- a/third_party/double-conversion/string-to-double.cc
+++ b/third_party/double-conversion/string-to-double.cc
@@ -52,9 +52,10 @@ namespace double_conversion {
 namespace {
 
 inline char ToLower(char ch) {
-  static const std::ctype<char>& cType =
+  /* static const std::ctype<char>& cType =
       std::use_facet<std::ctype<char> >(std::locale::classic());
-  return cType.tolower(ch);
+  return cType.tolower(ch); */
+  return tolower(ch);
 }
 
 inline char Pass(char ch) {