diff --git a/src/libcore/fmt/float.rs b/src/libcore/fmt/float.rs
index 87def375b202b..4825c2aa13264 100644
--- a/src/libcore/fmt/float.rs
+++ b/src/libcore/fmt/float.rs
@@ -21,7 +21,7 @@ fn float_to_decimal_common_exact<T>(fmt: &mut Formatter, num: &T,
 {
     unsafe {
         let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
-        let mut parts: [flt2dec::Part; 5] = mem::uninitialized();
+        let mut parts: [flt2dec::Part; 4] = mem::uninitialized();
         let formatted = flt2dec::to_exact_fixed_str(flt2dec::strategy::grisu::format_exact,
                                                     *num, sign, precision,
                                                     false, &mut buf, &mut parts);
@@ -39,7 +39,7 @@ fn float_to_decimal_common_shortest<T>(fmt: &mut Formatter,
     unsafe {
         // enough for f32 and f64
         let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
-        let mut parts: [flt2dec::Part; 5] = mem::uninitialized();
+        let mut parts: [flt2dec::Part; 4] = mem::uninitialized();
         let formatted = flt2dec::to_shortest_str(flt2dec::strategy::grisu::format_shortest,
                                                  *num, sign, 0, false, &mut buf, &mut parts);
         fmt.pad_formatted_parts(&formatted)
@@ -75,7 +75,7 @@ fn float_to_exponential_common_exact<T>(fmt: &mut Formatter, num: &T,
 {
     unsafe {
         let mut buf: [u8; 1024] = mem::uninitialized(); // enough for f32 and f64
-        let mut parts: [flt2dec::Part; 7] = mem::uninitialized();
+        let mut parts: [flt2dec::Part; 6] = mem::uninitialized();
         let formatted = flt2dec::to_exact_exp_str(flt2dec::strategy::grisu::format_exact,
                                                   *num, sign, precision,
                                                   upper, &mut buf, &mut parts);
@@ -94,7 +94,7 @@ fn float_to_exponential_common_shortest<T>(fmt: &mut Formatter,
     unsafe {
         // enough for f32 and f64
         let mut buf: [u8; flt2dec::MAX_SIG_DIGITS] = mem::uninitialized();
-        let mut parts: [flt2dec::Part; 7] = mem::uninitialized();
+        let mut parts: [flt2dec::Part; 6] = mem::uninitialized();
         let formatted = flt2dec::to_shortest_exp_str(flt2dec::strategy::grisu::format_shortest,
                                                      *num, sign, (0, 0), upper,
                                                      &mut buf, &mut parts);
diff --git a/src/libcore/num/flt2dec/mod.rs b/src/libcore/num/flt2dec/mod.rs
index 5123e42df61ca..74b9e7bf37d51 100644
--- a/src/libcore/num/flt2dec/mod.rs
+++ b/src/libcore/num/flt2dec/mod.rs
@@ -410,8 +410,8 @@ fn determine_sign(sign: Sign, decoded: &FullDecoded, negative: bool) -> &'static
 /// it will only print given digits and nothing else.
 ///
 /// The byte buffer should be at least `MAX_SIG_DIGITS` bytes long.
-/// There should be at least 5 parts available, due to the worst case like
-/// `[+][0.][0000][45][0000]` with `frac_digits = 10`.
+/// There should be at least 4 parts available, due to the worst case like
+/// `[+][0.][0000][2][0000]` with `frac_digits = 10`.
 pub fn to_shortest_str<'a, T, F>(mut format_shortest: F, v: T,
                                  sign: Sign, frac_digits: usize, _upper: bool,
                                  buf: &'a mut [u8], parts: &'a mut [Part<'a>]) -> Formatted<'a>
@@ -465,8 +465,8 @@ pub fn to_shortest_str<'a, T, F>(mut format_shortest: F, v: T,
 /// cannot be in this range, avoiding any confusion.
 ///
 /// The byte buffer should be at least `MAX_SIG_DIGITS` bytes long.
-/// There should be at least 7 parts available, due to the worst case like
-/// `[+][1][.][2345][e][-][67]`.
+/// There should be at least 6 parts available, due to the worst case like
+/// `[+][1][.][2345][e][-][6]`.
 pub fn to_shortest_exp_str<'a, T, F>(mut format_shortest: F, v: T,
                                      sign: Sign, dec_bounds: (i16, i16), upper: bool,
                                      buf: &'a mut [u8], parts: &'a mut [Part<'a>]) -> Formatted<'a>
@@ -544,8 +544,8 @@ fn estimate_max_buf_len(exp: i16) -> usize {
 /// The byte buffer should be at least `ndigits` bytes long unless `ndigits` is
 /// so large that only the fixed number of digits will be ever written.
 /// (The tipping point for `f64` is about 800, so 1000 bytes should be enough.)
-/// There should be at least 7 parts available, due to the worst case like
-/// `[+][1][.][2345][e][-][67]`.
+/// There should be at least 6 parts available, due to the worst case like
+/// `[+][1][.][2345][e][-][6]`.
 pub fn to_exact_exp_str<'a, T, F>(mut format_exact: F, v: T,
                                   sign: Sign, ndigits: usize, upper: bool,
                                   buf: &'a mut [u8], parts: &'a mut [Part<'a>]) -> Formatted<'a>
@@ -600,8 +600,8 @@ pub fn to_exact_exp_str<'a, T, F>(mut format_exact: F, v: T,
 /// The byte buffer should be enough for the output unless `frac_digits` is
 /// so large that only the fixed number of digits will be ever written.
 /// (The tipping point for `f64` is about 800, and 1000 bytes should be enough.)
-/// There should be at least 5 parts available, due to the worst case like
-/// `[+][0.][0000][45][0000]` with `frac_digits = 10`.
+/// There should be at least 4 parts available, due to the worst case like
+/// `[+][0.][0000][2][0000]` with `frac_digits = 10`.
 pub fn to_exact_fixed_str<'a, T, F>(mut format_exact: F, v: T,
                                     sign: Sign, frac_digits: usize, _upper: bool,
                                     buf: &'a mut [u8], parts: &'a mut [Part<'a>]) -> Formatted<'a>