diff --git a/cli/options.go b/cli/options.go
index 78fc0f0..afd0a4e 100644
--- a/cli/options.go
+++ b/cli/options.go
@@ -38,8 +38,11 @@ var boolWords = map[string]bool{
 }
 
 // boolWord reports a value's truth and whether it is a recognised boolean word.
+// Whitespace is trimmed (aria2 strips config values too), but case is
+// significant: aria2 rejects "True"/"TRUE", so the match is against exactly
+// "true"/"false".
 func boolWord(s string) (val, ok bool) {
-	val, ok = boolWords[strings.ToLower(strings.TrimSpace(s))]
+	val, ok = boolWords[strings.TrimSpace(s)]
 	return val, ok
 }
 
diff --git a/cli/parse_test.go b/cli/parse_test.go
index caeaea3..f359e0f 100644
--- a/cli/parse_test.go
+++ b/cli/parse_test.go
@@ -139,14 +139,16 @@ func TestValidateFloatNonNegative(t *testing.T) {
 
 func TestValidateBool(t *testing.T) {
 	b := byLong["enable-dht"]
-	// aria2 accepts only true/false; the invented yes/no/1/0/on/off spellings
-	// were removed, so they must now fail validation.
-	for _, ok := range []string{"true", "false"} {
+	// aria2 accepts only literal true/false (case-sensitive) but trims
+	// surrounding whitespace; match that exactly.
+	for _, ok := range []string{"true", "false", " true ", "false\t"} {
 		if err := validate(b, ok); err != nil {
 			t.Errorf("validate bool %q: %v", ok, err)
 		}
 	}
-	for _, bad := range []string{"yes", "no", "1", "0", "on", "off", "flase"} {
+	// The invented spellings and any case variant must now fail.
+	for _, bad := range []string{"yes", "no", "1", "0", "on", "off", "flase",
+		"True", "TRUE", "tRuE", "False", "FALSE"} {
 		if err := validate(b, bad); err == nil {
 			t.Errorf("validate bool %q: want error (only true/false accepted)", bad)
 		}