diff --git a/README.adoc b/README.adoc
index ddf6c3b..b43ccd7 100644
--- a/README.adoc
+++ b/README.adoc
@@ -11788,7 +11788,7 @@ Conclusion:
 
 [options="header"]
 |===
-|byte |word |long |quad |octa
+|.byte |.word |.long |.quad |.octa
 
 |x86
 |1
@@ -11813,7 +11813,7 @@ Conclusion:
 
 |===
 
-and also keep in mind that:
+and also keep in mind that according to the manual:
 
 * `.int` is the same as `.long`
 * `.hword` is the same as `.short` which is usually the same as `.word`
diff --git a/userland/arch/x86_64/common_arch.h b/userland/arch/x86_64/common_arch.h
index 1ce486c..aa035ea 100644
--- a/userland/arch/x86_64/common_arch.h
+++ b/userland/arch/x86_64/common_arch.h
@@ -3,6 +3,8 @@
 #ifndef COMMON_ARCH_H
 #define COMMON_ARCH_H
 
+/* This and other macros may make C function calls, and therefore can destroy
+ * non-callee saved registers. */
 #define ASSERT_EQ(general1, general2) \
     mov general2, %rdi; \
     push %rdi; \
diff --git a/userland/arch/x86_64/gas_data_sizes.S b/userland/arch/x86_64/gas_data_sizes.S
index 2219ea9..dc13f49 100644
--- a/userland/arch/x86_64/gas_data_sizes.S
+++ b/userland/arch/x86_64/gas_data_sizes.S
@@ -4,8 +4,9 @@
 
 ENTRY
 #define ASSERT_DIFF(label1, label2, result) \
-    mov $label2, %rax; \
-    sub $label1, %rax; \
+    lea label2(%rip), %rax; \
+    lea label1(%rip), %rbx; \
+    sub %rbx, %rax; \
     ASSERT_EQ(%rax, $result)
 
     ASSERT_DIFF(mybyte, myword, 1)