diff --git a/internal/addrs/instance_key.go b/internal/addrs/instance_key.go
index ff128be5b4..2d46bfcbe0 100644
--- a/internal/addrs/instance_key.go
+++ b/internal/addrs/instance_key.go
@@ -2,6 +2,8 @@ package addrs
 
 import (
 	"fmt"
+	"strings"
+	"unicode"
 
 	"github.com/zclconf/go-cty/cty"
 	"github.com/zclconf/go-cty/cty/gocty"
@@ -72,9 +74,10 @@ func (k StringKey) instanceKeySigil() {
 }
 
 func (k StringKey) String() string {
-	// FIXME: This isn't _quite_ right because Go's quoted string syntax is
-	// slightly different than HCL's, but we'll accept it for now.
-	return fmt.Sprintf("[%q]", string(k))
+	// We use HCL's quoting syntax here so that we can in principle parse
+	// an address constructed by this package as if it were an HCL
+	// traversal, even if the string contains HCL's own metacharacters.
+	return fmt.Sprintf("[%s]", toHCLQuotedString(string(k)))
 }
 
 func (k StringKey) Value() cty.Value {
@@ -133,3 +136,56 @@ const (
 	IntKeyType    InstanceKeyType = 'I'
 	StringKeyType InstanceKeyType = 'S'
 )
+
+// toHCLQuotedString is a helper which formats the given string in a way that
+// HCL's expression parser would treat as a quoted string template.
+//
+// This includes:
+//   - Adding quote marks at the start and the end.
+//   - Using backslash escapes as needed for characters that cannot be represented directly.
+//   - Escaping anything that would be treated as a template interpolation or control sequence.
+func toHCLQuotedString(s string) string {
+	// This is an adaptation of a similar function inside the hclwrite package,
+	// inlined here because hclwrite's version generates HCL tokens but we
+	// only need normal strings.
+	if len(s) == 0 {
+		return `""`
+	}
+	var buf strings.Builder
+	buf.WriteByte('"')
+	for i, r := range s {
+		switch r {
+		case '\n':
+			buf.WriteString(`\n`)
+		case '\r':
+			buf.WriteString(`\r`)
+		case '\t':
+			buf.WriteString(`\t`)
+		case '"':
+			buf.WriteString(`\"`)
+		case '\\':
+			buf.WriteString(`\\`)
+		case '$', '%':
+			buf.WriteRune(r)
+			remain := s[i+1:]
+			if len(remain) > 0 && remain[0] == '{' {
+				// Double up our template introducer symbol to escape it.
+				buf.WriteRune(r)
+			}
+		default:
+			if !unicode.IsPrint(r) {
+				var fmted string
+				if r < 65536 {
+					fmted = fmt.Sprintf("\\u%04x", r)
+				} else {
+					fmted = fmt.Sprintf("\\U%08x", r)
+				}
+				buf.WriteString(fmted)
+			} else {
+				buf.WriteRune(r)
+			}
+		}
+	}
+	buf.WriteByte('"')
+	return buf.String()
+}
diff --git a/internal/addrs/instance_key_test.go b/internal/addrs/instance_key_test.go
new file mode 100644
index 0000000000..0d12888bf0
--- /dev/null
+++ b/internal/addrs/instance_key_test.go
@@ -0,0 +1,75 @@
+package addrs
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestInstanceKeyString(t *testing.T) {
+	tests := []struct {
+		Key  InstanceKey
+		Want string
+	}{
+		{
+			IntKey(0),
+			`[0]`,
+		},
+		{
+			IntKey(5),
+			`[5]`,
+		},
+		{
+			StringKey(""),
+			`[""]`,
+		},
+		{
+			StringKey("hi"),
+			`["hi"]`,
+		},
+		{
+			StringKey("0"),
+			`["0"]`, // intentionally distinct from IntKey(0)
+		},
+		{
+			// Quotes must be escaped
+			StringKey(`"`),
+			`["\""]`,
+		},
+		{
+			// Escape sequences must themselves be escaped
+			StringKey(`\r\n`),
+			`["\\r\\n"]`,
+		},
+		{
+			// Template interpolation sequences "${" must be escaped.
+			StringKey(`${hello}`),
+			`["$${hello}"]`,
+		},
+		{
+			// Template control sequences "%{" must be escaped.
+			StringKey(`%{ for something in something }%{ endfor }`),
+			`["%%{ for something in something }%%{ endfor }"]`,
+		},
+		{
+			// Dollar signs that aren't followed by { are not interpolation sequences
+			StringKey(`$hello`),
+			`["$hello"]`,
+		},
+		{
+			// Percent signs that aren't followed by { are not control sequences
+			StringKey(`%hello`),
+			`["%hello"]`,
+		},
+	}
+
+	for _, test := range tests {
+		testName := fmt.Sprintf("%#v", test.Key)
+		t.Run(testName, func(t *testing.T) {
+			got := test.Key.String()
+			want := test.Want
+			if got != want {
+				t.Errorf("wrong result\nreciever: %s\ngot:      %s\nwant:     %s", testName, got, want)
+			}
+		})
+	}
+}