diff --git a/arch/avr/src/at91uc3/at91uc3_config.h b/arch/avr/src/at91uc3/at91uc3_config.h
index feac188b85b..dbe6403ec3a 100755
--- a/arch/avr/src/at91uc3/at91uc3_config.h
+++ b/arch/avr/src/at91uc3/at91uc3_config.h
@@ -65,17 +65,52 @@
 #  undef CONFIG_AVR32_USART2
 #endif
 
+/* Not all USART features are supported on all chips or all USARTS */
+
+#ifdef CONFIG_ARCH_CHIP_AT91UC3B
+# undef CONFIG_AVR32_USART0_RS485
+# undef CONFIG_AVR32_USART0_MAN
+# undef CONFIG_AVR32_USART0_MODEM
+# undef CONFIG_AVR32_USART0_IRDA
+# undef CONFIG_AVR32_USART0_ISO786
+# undef CONFIG_AVR32_USART1_RS485
+# undef CONFIG_AVR32_USART2_RS485
+# undef CONFIG_AVR32_USART2_MAN
+# undef CONFIG_AVR32_USART2_MODEM
+# undef CONFIG_AVR32_USART2_IRDA
+# undef CONFIG_AVR32_USART2_ISO786
+#endif
+
+/* Disable configurations if USART not selected in configuration file */
+
 #ifndef CONFIG_AVR32_USART0
 #  undef CONFIG_AVR32_USART0_RS232
 #  undef CONFIG_AVR32_USART0_SPI
+#  undef CONFIG_AVR32_USART0_RS485
+#  undef CONFIG_AVR32_USART0_MAN
+#  undef CONFIG_AVR32_USART0_MODEM
+#  undef CONFIG_AVR32_USART0_IRDA
+#  undef CONFIG_AVR32_USART0_ISO786
 #endif
+
 #ifndef CONFIG_AVR32_USART1
 #  undef CONFIG_AVR32_USART1_RS232
 #  undef CONFIG_AVR32_USART1_SPI
+#  undef CONFIG_AVR32_USART1_RS485
+#  undef CONFIG_AVR32_USART1_MAN
+#  undef CONFIG_AVR32_USART1_MODEM
+#  undef CONFIG_AVR32_USART1_IRDA
+#  undef CONFIG_AVR32_USART1_ISO786
 #endif
+
 #ifndef CONFIG_AVR32_USART2
 #  undef CONFIG_AVR32_USART2_RS232
 #  undef CONFIG_AVR32_USART2_SPI
+#  undef CONFIG_AVR32_USART2_RS485
+#  undef CONFIG_AVR32_USART2_MAN
+#  undef CONFIG_AVR32_USART2_MODEM
+#  undef CONFIG_AVR32_USART2_IRDA
+#  undef CONFIG_AVR32_USART2_ISO786
 #endif
 
 /* Is any UART configured? */