diff --git a/src/KeyName.cxx b/src/KeyName.cxx
index 84b454e1..8d9b3bbd 100644
--- a/src/KeyName.cxx
+++ b/src/KeyName.cxx
@@ -60,11 +60,9 @@ GetKeyName(int key) noexcept
 {
 	static char buf[32];
 
-	for (int i = 0; i < 64; ++i) {
-		if (key == KEY_F(i)) {
-			snprintf(buf, sizeof(buf), "F%u", i);
-			return buf;
-		}
+	if (IsFKey(key)) {
+		snprintf(buf, sizeof(buf), "F%u", key - KEY_F0);
+		return buf;
 	}
 
 	const char *name = keyname(key);
@@ -132,11 +130,9 @@ GetLocalizedKeyName(int key) noexcept
 
 	static char buf[32];
 
-	for (int i = 0; i <= 63; i++) {
-		if (key == KEY_F(i)) {
-			snprintf(buf, sizeof(buf), "F%d", i );
-			return buf;
-		}
+	if (IsFKey(key)) {
+		snprintf(buf, sizeof(buf), "F%u", key - KEY_F0);
+		return buf;
 	}
 
 	const char *name = keyname(key);
diff --git a/src/dialogs/TextInputDialog.cxx b/src/dialogs/TextInputDialog.cxx
index 5eb53195..c548405e 100644
--- a/src/dialogs/TextInputDialog.cxx
+++ b/src/dialogs/TextInputDialog.cxx
@@ -220,11 +220,8 @@ TextInputDialog::OnKey(const Window window, int key)
 	}
 
 	/* check if key is a function key */
-	for (size_t i = 0; i < 63; i++)
-		if (key == (int)KEY_F(i)) {
-			key = KEY_F(1);
-			i = 64;
-		}
+	if (IsFKey(key))
+		return false;
 
 	switch (key) {
 	case KEY_TAB:
@@ -331,7 +328,6 @@ TextInputDialog::OnKey(const Window window, int key)
 	case KEY_IC:
 	case KEY_PPAGE:
 	case KEY_NPAGE:
-	case KEY_F(1):
 		/* ignore char */
 		break;
 	default:
diff --git a/src/ui/Keys.hxx b/src/ui/Keys.hxx
index 469c7cd1..57b11688 100644
--- a/src/ui/Keys.hxx
+++ b/src/ui/Keys.hxx
@@ -15,3 +15,9 @@ enum : int {
 	KEY_ESCAPE = 0x1b,
 	KEY_BACKSPACE3 = 0x7f,
 };
+
+constexpr bool
+IsFKey(int key) noexcept
+{
+	return key >= KEY_F(0) && key <= KEY_F(63);
+}