diff --git a/lib/linebuffer.c b/lib/linebuffer.c
index 4124bbcb37..9c8e12ab32 100644
--- a/lib/linebuffer.c
+++ b/lib/linebuffer.c
@@ -31,6 +31,19 @@
 # include "unlocked-io.h"
 #endif
 
+/* END_OF_ARRAY(array,n) returns a pointer past the last element of the array
+   ARRAY that has N elements.
+   For clang, it uses a conditional expression that avoids adding 0 to a null
+   pointer, which is undefined according to ISO C 23 § 6.5.6.(9) and which
+   triggers an error in clang's undefined-behaviour sanitizer.  When no
+   sanitizer is in effect, clang optimizes this conditional expression to
+   exactly the same code.  */
+#if defined __clang__
+# define END_OF_ARRAY(array,n) ((n) ? (array) + (n) : (array))
+#else
+# define END_OF_ARRAY(array,n) ((array) + (n))
+#endif
+
 /* Initialize linebuffer LINEBUFFER for use. */
 
 void
@@ -62,7 +75,7 @@ readlinebuffer_delim (struct linebuffer *linebuffer, FILE *stream,

   char *buffer = linebuffer->buffer;
   char *p = linebuffer->buffer;
-  char *end = buffer + linebuffer->size; /* Sentinel. */
+  char *end = END_OF_ARRAY (buffer, linebuffer->size); /* Sentinel. */
   int c;

   do
diff --git a/lib/mpsort.c b/lib/mpsort.c
index 32cc5e1f82..2741d7199d 100644
--- a/lib/mpsort.c
+++ b/lib/mpsort.c
@@ -23,6 +23,19 @@
 
 #include <string.h>
 
+/* END_OF_ARRAY(array,n) returns a pointer past the last element of the array
+   ARRAY that has N elements.
+   For clang, it uses a conditional expression that avoids adding 0 to a null
+   pointer, which is undefined according to ISO C 23 § 6.5.6.(9) and which
+   triggers an error in clang's undefined-behaviour sanitizer.  When no
+   sanitizer is in effect, clang optimizes this conditional expression to
+   exactly the same code.  */
+#if defined __clang__
+# define END_OF_ARRAY(array,n) ((n) ? (array) + (n) : (array))
+#else
+# define END_OF_ARRAY(array,n) ((array) + (n))
+#endif
+
 /* The type of qsort-style comparison functions.  */
 
 typedef int (*comparison_function) (void const *, void const *);
@@ -152,5 +165,5 @@ mpsort_with_tmp (void const **restrict base, size_t n,
 void
 mpsort (void const **base, size_t n, comparison_function cmp)
 {
-  mpsort_with_tmp (base, n, base + n, cmp);
+  mpsort_with_tmp (base, n, END_OF_ARRAY (base, n), cmp);
 }