diff --git a/src/go/constant/value.go b/src/go/constant/value.go
index f8d03cf3756c1..ae300c7c13c91 100644
--- a/src/go/constant/value.go
+++ b/src/go/constant/value.go
@@ -200,7 +200,13 @@ func (x floatVal) String() string {
 	// Use exact fmt formatting if in float64 range (common case):
 	// proceed if f doesn't underflow to 0 or overflow to inf.
 	if x, _ := f.Float64(); f.Sign() == 0 == (x == 0) && !math.IsInf(x, 0) {
-		return fmt.Sprintf("%.6g", x)
+		s := fmt.Sprintf("%.6g", x)
+		if !f.IsInt() && strings.IndexByte(s, '.') < 0 {
+			// f is not an integer, but its string representation
+			// doesn't reflect that. Use more digits. See issue 56220.
+			s = fmt.Sprintf("%g", x)
+		}
+		return s
 	}
 
 	// Out of float64 range. Do approximate manual to decimal
diff --git a/test/fixedbugs/issue56220.go b/test/fixedbugs/issue56220.go
new file mode 100644
index 0000000000000..3cb5210e894a3
--- /dev/null
+++ b/test/fixedbugs/issue56220.go
@@ -0,0 +1,15 @@
+// errorcheck
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func f() int {
+	return int(1 - .0000001) // ERROR "cannot convert 1 - \.0000001 \(untyped float constant 0\.9999999\) to type int"
+}
+
+func g() int64 {
+	return int64((float64(0.03) - float64(0.02)) * 1_000_000) // ERROR "cannot convert \(float64\(0\.03\) - float64\(0\.02\)\) \* 1_000_000 \(constant 9999\.999999999998 of type float64\) to type int64"
+}