3 files changed, 29 insertions, 3 deletions
diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index ce76252340..ada85e9fed 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -244,7 +244,9 @@ func readFloat(s string) (mantissa uint64, exp int, neg, trunc, ok bool) {
 		return
 	}
 
-	exp = dp - ndMant
+	if mantissa != 0 {
+		exp = dp - ndMant
+	}
 	ok = true
 	return
 
diff --git a/src/strconv/atof_test.go b/src/strconv/atof_test.go
index 9f70cc1fd7..0a89c3e0bf 100644
--- a/src/strconv/atof_test.go
+++ b/src/strconv/atof_test.go
@@ -42,6 +42,30 @@ var atoftests = []atofTest{
 	{"1e-20", "1e-20", nil},
 	{"625e-3", "0.625", nil},
 
+	// zeros
+	{"0", "0", nil},
+	{"0e0", "0", nil},
+	{"-0e0", "-0", nil},
+	{"+0e0", "0", nil},
+	{"0e-0", "0", nil},
+	{"-0e-0", "-0", nil},
+	{"+0e-0", "0", nil},
+	{"0e+0", "0", nil},
+	{"-0e+0", "-0", nil},
+	{"+0e+0", "0", nil},
+	{"0e+01234567890123456789", "0", nil},
+	{"0.00e-01234567890123456789", "0", nil},
+	{"-0e+01234567890123456789", "-0", nil},
+	{"-0.00e-01234567890123456789", "-0", nil},
+	{"0e291", "0", nil}, // issue 15364
+	{"0e292", "0", nil}, // issue 15364
+	{"0e347", "0", nil}, // issue 15364
+	{"0e348", "0", nil}, // issue 15364
+	{"-0e291", "-0", nil},
+	{"-0e292", "-0", nil},
+	{"-0e347", "-0", nil},
+	{"-0e348", "-0", nil},
+
 	// NaNs
 	{"nan", "NaN", nil},
 	{"NaN", "NaN", nil},
diff --git a/src/strconv/extfloat.go b/src/strconv/extfloat.go
index 019b4eebdc..7033e96c39 100644
--- a/src/strconv/extfloat.go
+++ b/src/strconv/extfloat.go
@@ -311,9 +311,9 @@ func (f *extFloat) AssignDecimal(mantissa uint64, exp10 int, neg bool, trunc boo
 	var extrabits uint
 	if f.exp <= denormalExp {
 		// f.mant * 2^f.exp is smaller than 2^(flt.bias+1).
-		extrabits = uint(63 - flt.mantbits + 1 + uint(denormalExp-f.exp))
+		extrabits = 63 - flt.mantbits + 1 + uint(denormalExp-f.exp)
 	} else {
-		extrabits = uint(63 - flt.mantbits)
+		extrabits = 63 - flt.mantbits
 	}
 
 	halfway := uint64(1) << (extrabits - 1)