diff --git a/integrations/cobra/cobra_usage_test.go b/integrations/cobra/cobra_usage_test.go
index 4684b7b5a..28f21dbf1 100644
--- a/integrations/cobra/cobra_usage_test.go
+++ b/integrations/cobra/cobra_usage_test.go
@@ -350,6 +350,29 @@ func TestStringDefaultZero(t *testing.T) {
 	assertContains(t, got, `default="0"`)
 }
 
+// TestDefaultsQuotedWhenNotIdentifiers checks that defaults KDL would read as a
+// boolean, null, or number are quoted so they stay strings.
+func TestDefaultsQuotedWhenNotIdentifiers(t *testing.T) {
+	cmd := &cobra.Command{Use: "app"}
+	cmd.Flags().Bool("enabled", true, "Enable the feature")
+	cmd.Flags().Int("parallel", -1, "Maximum parallelism")
+	cmd.Flags().Float64("ratio", -0.5, "Ratio")
+	cmd.Flags().String("sign", "+1", "Signed")
+	cmd.Flags().String("nothing", "null", "Null word")
+	cmd.Flags().String("infinite", "inf", "Inf word")
+	cmd.Flags().String("list", "[a]", "Brackets")
+
+	got := Generate(cmd)
+
+	assertContains(t, got, `default="true"`)
+	assertContains(t, got, `default="-1"`)
+	assertContains(t, got, `default="-0.5"`)
+	assertContains(t, got, `default="+1"`)
+	assertContains(t, got, `default="null"`)
+	assertContains(t, got, `default="inf"`)
+	assertContains(t, got, `default="[a]"`)
+}
+
 // TestSpecialCharacterEscaping checks that kdlQuoteAlways escapes newlines, tabs,
 // carriage returns, backslashes, and double quotes.
 func TestSpecialCharacterEscaping(t *testing.T) {
diff --git a/integrations/cobra/kdl.go b/integrations/cobra/kdl.go
index 1d2199f95..180e00de7 100644
--- a/integrations/cobra/kdl.go
+++ b/integrations/cobra/kdl.go
@@ -353,9 +353,19 @@ func needsQuoting(s string) bool {
 	if s[0] >= '0' && s[0] <= '9' {
 		return true
 	}
+	// A sign followed by a digit (or a dot, which is quoted below) reads as a
+	// number, so "-1" and "+1" cannot be bare identifiers either.
+	if (s[0] == '-' || s[0] == '+') && len(s) > 1 && (s[1] >= '0' && s[1] <= '9' || s[1] == '.') {
+		return true
+	}
+	// Keyword-looking values would be parsed as a boolean, null or number.
+	switch s {
+	case "true", "false", "null", "inf", "-inf", "nan":
+		return true
+	}
 	for _, c := range s {
 		switch c {
-		case ' ', '\t', '\n', '\r', '"', '\\', '/', '(', ')', '{', '}', ';', '=', '#', '.', ',', ':':
+		case ' ', '\t', '\n', '\r', '"', '\\', '/', '(', ')', '[', ']', '{', '}', ';', '=', '#', '.', ',', ':':
 			return true
 		}
 	}