diff --git a/src/jemalloc.c b/src/jemalloc.c
index 7cf1487a..6ed3d4e2 100644
--- a/src/jemalloc.c
+++ b/src/jemalloc.c
@@ -2275,6 +2275,9 @@ ixallocx_prof(tsd_t *tsd, void *ptr, size_t old_usize, size_t size,
 	prof_tctx_t *old_tctx, *tctx;
 
 	old_tctx = prof_tctx_get(ptr);
+	/* Clamp extra if necessary to avoid (size + extra) overflow. */
+	if (unlikely(size + extra > HUGE_MAXCLASS))
+		extra = HUGE_MAXCLASS - size;
 	/*
 	 * usize isn't knowable before ixalloc() returns when extra is non-zero.
 	 * Therefore, compute its maximum possible value and use that in