diff --git a/lab004/firmware/Makefile b/lab004/firmware/Makefile
index 577de49..9a0990b 100644
--- a/lab004/firmware/Makefile
+++ b/lab004/firmware/Makefile
@@ -3,7 +3,7 @@ BUILD_DIR=../build/
 include $(BUILD_DIR)/software/include/generated/variables.mak
 include $(SOC_DIRECTORY)/software/common.mak
 
-OBJECTS=isr.o main.o
+OBJECTS=isr.o main.o crt0.o
 
 all: firmware.bin
 
diff --git a/lab004/firmware/linker.ld b/lab004/firmware/linker.ld
index 36af682..fba8124 100644
--- a/lab004/firmware/linker.ld
+++ b/lab004/firmware/linker.ld
@@ -10,6 +10,12 @@ SECTIONS
 	.text :
 	{
 		_ftext = .;
+		/* Make sure crt0 files come first, and they, and the isr */
+		/* don't get disposed of by greedy optimisation */
+		*crt0*(.text)
+		KEEP(*crt0*(.text))
+		KEEP(*(.text.isr))
+
 		*(.text .stub .text.* .gnu.linkonce.t.*)
 		_etext = .;
 	} > main_ram