diff --git a/board/chell/board.h b/board/chell/board.h
index 9490bec054..b875255219 100644
--- a/board/chell/board.h
+++ b/board/chell/board.h
@@ -46,6 +46,9 @@
 #undef CONFIG_RO_SIZE
 #define CONFIG_RO_SIZE (100 * 1024)
 #define CONFIG_SCI_GPIO GPIO_PCH_SCI_L
+/* We're space constrained on Chell, so reduce the UART TX buffer size. */
+#undef CONFIG_UART_TX_BUF_SIZE
+#define CONFIG_UART_TX_BUF_SIZE 512
 #define CONFIG_USB_CHARGER
 #define CONFIG_USB_MUX_PS8740
 #define CONFIG_USB_POWER_DELIVERY
diff --git a/board/glados/board.h b/board/glados/board.h
index e3f44a3ccb..90503cfa35 100644
--- a/board/glados/board.h
+++ b/board/glados/board.h
@@ -54,6 +54,9 @@
 #undef CONFIG_RO_SIZE
 #define CONFIG_RO_SIZE (100 * 1024)
 #define CONFIG_SCI_GPIO GPIO_PCH_SCI_L
+/* We're space constrained on GLaDOS, so reduce the UART TX buffer size. */
+#undef CONFIG_UART_TX_BUF_SIZE
+#define CONFIG_UART_TX_BUF_SIZE 512
 #define CONFIG_USB_CHARGER
 #define CONFIG_USB_MUX_PI3USB30532
 #define CONFIG_USB_MUX_PS8740
diff --git a/board/kunimitsu/board.h b/board/kunimitsu/board.h
index cf43dc8b8a..3f66fe26ac 100644
--- a/board/kunimitsu/board.h
+++ b/board/kunimitsu/board.h
@@ -77,6 +77,9 @@
 #undef CONFIG_RO_SIZE
 #define CONFIG_RO_SIZE (100 * 1024)
 #define CONFIG_SCI_GPIO GPIO_PCH_SCI_L
+/* We're space constrained on Kunimitsu, so reduce the UART TX buffer size. */
+#undef CONFIG_UART_TX_BUF_SIZE
+#define CONFIG_UART_TX_BUF_SIZE 512
 #define CONFIG_USB_CHARGER
 #define CONFIG_USB_MUX_PI3USB30532
 #define CONFIG_USB_POWER_DELIVERY