diff --git a/source/preprocessor.tex b/source/preprocessor.tex
index 6e9bea8816..8081fc6e73 100644
--- a/source/preprocessor.tex
+++ b/source/preprocessor.tex
@@ -80,7 +80,9 @@
 
 \begin{bnf}\obeyspaces
 \nontermdef{elif-group}\br
-    \terminal{\# elif   } constant-expression new-line \opt{group}
+    \terminal{\# elif    } constant-expression new-line \opt{group}\br
+    \terminal{\# elifdef } constant-expression new-line \opt{group}\br
+    \terminal{\# elifndef} constant-expression new-line \opt{group}
 \end{bnf}
 
 \begin{bnf}\obeyspaces
@@ -399,7 +401,9 @@
 \end{floattable}
 
 \pnum
-The \tcode{\#ifdef} and \tcode{\#ifndef} directives, and
+The
+\tcode{\#ifdef}, \tcode{\#ifndef}, \tcode{\#elifdef}, and \tcode{\#elifndef}
+directives, and
 the \tcode{defined} conditional inclusion operator,
 shall treat \xname{has_include} and \xname{has_cpp_attribute}
 as if they were the names of defined macros.
@@ -491,20 +495,21 @@
 \pnum
 Preprocessing directives of the forms
 \begin{ncsimplebnf}\obeyspaces
-\terminal{\# ifdef  } identifier new-line \opt{group}\br
+\terminal{\# ifdef   } identifier new-line \opt{group}\br
 \indextext{\idxcode{\#ifdef}}%
-\terminal{\# ifndef } identifier new-line \opt{group}
+\terminal{\# ifndef  } identifier new-line \opt{group}\br
 \indextext{\idxcode{\#ifndef}}%
+\terminal{\# elifdef } identifier new-line \opt{group}\br
+\indextext{\idxcode{\#elifdef}}%
+\terminal{\# elifndef} identifier new-line \opt{group}
+\indextext{\idxcode{\#elifndef}}%
 \end{ncsimplebnf}
 check whether the identifier is or is not currently defined as a macro name.
 Their conditions are equivalent to
-\tcode{\#if}
-\tcode{defined}
-\grammarterm{identifier}
-and
-\tcode{\#if}
-\tcode{!defined}
-\grammarterm{identifier}
+\tcode{\#if} \tcode{defined} \grammarterm{identifier},
+\tcode{\#if} \tcode{!defined} \grammarterm{identifier},
+\tcode{\#elif} \tcode{defined} \grammarterm{identifier}, and
+\tcode{\#elif} \tcode{!defined} \grammarterm{identifier},
 respectively.
 
 \pnum