diff --git a/include/fmt/format.h b/include/fmt/format.h
index d635b91d..dc2336cd 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -2787,7 +2787,8 @@ void basic_writer<Range>::write_double(T value, const format_specs &spec) {
     if (sign) {
       *reserve(1) = sign;
       sign = 0;
-      --as.width_;
+      if (as.width_)
+        --as.width_;
     }
     as.align_ = ALIGN_RIGHT;
   } else {
diff --git a/test/format-test.cc b/test/format-test.cc
index 62bf224e..17dedd3b 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -532,6 +532,7 @@ TEST(FormatterTest, NumericAlign) {
       format_error, "format specifier requires numeric argument");
   EXPECT_THROW_MSG(format("{0:=8}", reinterpret_cast<void*>(0xface)),
       format_error, "format specifier requires numeric argument");
+  EXPECT_EQ(" 1", fmt::format("{:= }", 1.0));
 }
 
 TEST(FormatterTest, CenterAlign) {