diff --git a/doc/64bit.src b/doc/64bit.src
index 9a5fda64..4e24d557 100644
--- a/doc/64bit.src
+++ b/doc/64bit.src
@@ -62,6 +62,8 @@ In 64-bit mode, immediates and displacements are generally only 32
 bits wide.  NASM will therefore truncate most displacements and
 immediates to 32 bits.
 
+\S{id64imm} Immediate 64-bit Operands
+
 The only instruction which takes a full \i{64-bit immediate} is:
 
 \c      MOV reg64,imm64
@@ -97,6 +99,8 @@ instruction is able to reference a symbol anywhere in the 64-bit
 address space, whereas \c{LEA} is only able to access a symbol within
 within 2 GB of the instruction itself (see below.)
 
+\S{id64disp} 64-bit Displacements
+
 The only instructions which take a full \I{64-bit displacement}64-bit
 \e{displacement} is loading or storing, using \c{MOV}, \c{AL}, \c{AX},
 \c{EAX} or \c{RAX} (but no other registers) to an absolute 64-bit address.
diff --git a/doc/syntax.src b/doc/syntax.src
index 0eababcb..5969e875 100644
--- a/doc/syntax.src
+++ b/doc/syntax.src
@@ -1,5 +1,14 @@
 \C{Syntax} Syntax Quirks and Summaries
 
+\H{64moff} 64-bit \i{MOFFS}
+
+The moffs operand can be used with the \c{MOV} instruction, only using the A
+register (AL/AH, AX, EAX, RAX), and for non-64-bit operand size means to address
+memory at an offset from a segment. For \I{64-bit immediate} 64-bit operands it
+simply accesses memory at a specified offset (since segment based addressing is
+mostly unavailable in 64-bit mode). Syntax to use 64-bit offsets to address
+memory is showcased in \k{id64disp}.
+
 \H{spliteas} \i{Split EA} Addressing Syntax
 
 Instructions that use the mib operand, (that is memory addressed with a base