diff --git a/src/huge.c b/src/huge.c
index cecaf2df..6d86aed8 100644
--- a/src/huge.c
+++ b/src/huge.c
@@ -171,6 +171,16 @@ huge_ralloc(void *ptr, size_t oldsize, size_t size, size_t extra,
 				abort();
 			memcpy(ret, ptr, copysize);
 			chunk_dealloc_mmap(ptr, oldsize);
+		} else if (config_fill && zero == false && opt_junk && oldsize
+		    < newsize) {
+			/*
+			 * mremap(2) clobbers the original mapping, so
+			 * junk/zero filling is not preserved.  There is no
+			 * need to zero fill here, since any trailing
+			 * uninititialized memory is demand-zeroed by the
+			 * kernel, but junk filling must be redone.
+			 */
+			memset(ret + oldsize, 0xa5, newsize - oldsize);
 		}
 	} else
 #endif
diff --git a/test/unit/junk.c b/test/unit/junk.c
index e27db2fe..ef8f9c16 100644
--- a/test/unit/junk.c
+++ b/test/unit/junk.c
@@ -92,9 +92,12 @@ test_junk(size_t sz_min, size_t sz_max)
 			s = (char *)rallocx(s, sz+1, 0);
 			assert_ptr_not_null((void *)s,
 			    "Unexpected rallocx() failure");
-			assert_ptr_eq(most_recently_junked, junked,
-			    "Expected region of size %zu to be junk-filled",
-			    sz);
+			if (!config_mremap || sz+1 <= arena_maxclass) {
+				assert_ptr_eq(most_recently_junked, junked,
+				    "Expected region of size %zu to be "
+				    "junk-filled",
+				    sz);
+			}
 		}
 	}