diff --git a/include/jemalloc/internal/util.h b/include/jemalloc/internal/util.h
index 949a0e0a..a0c2203d 100644
--- a/include/jemalloc/internal/util.h
+++ b/include/jemalloc/internal/util.h
@@ -41,8 +41,8 @@
 #define	MALLOC_PRINTF_BUFSIZE	4096
 
 /* Junk fill patterns. */
-#define	JEMALLOC_ALLOC_JUNK	0xa5
-#define	JEMALLOC_FREE_JUNK	0x5a
+#define	JEMALLOC_ALLOC_JUNK	((uint8_t)0xa5)
+#define	JEMALLOC_FREE_JUNK	((uint8_t)0x5a)
 
 /*
  * Wrap a cpp argument that contains commas such that it isn't broken up into
diff --git a/test/unit/junk.c b/test/unit/junk.c
index f4e62261..fecf6fae 100644
--- a/test/unit/junk.c
+++ b/test/unit/junk.c
@@ -29,7 +29,7 @@ arena_dalloc_junk_small_intercept(void *ptr, arena_bin_info_t *bin_info)
 
 	arena_dalloc_junk_small_orig(ptr, bin_info);
 	for (i = 0; i < bin_info->reg_size; i++) {
-		assert_c_eq(((char *)ptr)[i], JEMALLOC_FREE_JUNK,
+		assert_u_eq(((uint8_t *)ptr)[i], JEMALLOC_FREE_JUNK,
 		    "Missing junk fill for byte %zu/%zu of deallocated region",
 		    i, bin_info->reg_size);
 	}
@@ -44,7 +44,7 @@ arena_dalloc_junk_large_intercept(void *ptr, size_t usize)
 
 	arena_dalloc_junk_large_orig(ptr, usize);
 	for (i = 0; i < usize; i++) {
-		assert_c_eq(((char *)ptr)[i], JEMALLOC_FREE_JUNK,
+		assert_u_eq(((uint8_t *)ptr)[i], JEMALLOC_FREE_JUNK,
 		    "Missing junk fill for byte %zu/%zu of deallocated region",
 		    i, usize);
 	}
@@ -69,7 +69,7 @@ huge_dalloc_junk_intercept(void *ptr, size_t usize)
 static void
 test_junk(size_t sz_min, size_t sz_max)
 {
-	char *s;
+	uint8_t *s;
 	size_t sz_prev, sz, i;
 
 	if (opt_junk_free) {
@@ -82,23 +82,23 @@ test_junk(size_t sz_min, size_t sz_max)
 	}
 
 	sz_prev = 0;
-	s = (char *)mallocx(sz_min, 0);
+	s = (uint8_t *)mallocx(sz_min, 0);
 	assert_ptr_not_null((void *)s, "Unexpected mallocx() failure");
 
 	for (sz = sallocx(s, 0); sz <= sz_max;
 	    sz_prev = sz, sz = sallocx(s, 0)) {
 		if (sz_prev > 0) {
-			assert_c_eq(s[0], 'a',
+			assert_u_eq(s[0], 'a',
 			    "Previously allocated byte %zu/%zu is corrupted",
 			    ZU(0), sz_prev);
-			assert_c_eq(s[sz_prev-1], 'a',
+			assert_u_eq(s[sz_prev-1], 'a',
 			    "Previously allocated byte %zu/%zu is corrupted",
 			    sz_prev-1, sz_prev);
 		}
 
 		for (i = sz_prev; i < sz; i++) {
 			if (opt_junk_alloc) {
-				assert_c_eq(s[i], JEMALLOC_ALLOC_JUNK,
+				assert_u_eq(s[i], JEMALLOC_ALLOC_JUNK,
 				    "Newly allocated byte %zu/%zu isn't "
 				    "junk-filled", i, sz);
 			}
@@ -107,7 +107,7 @@ test_junk(size_t sz_min, size_t sz_max)
 
 		if (xallocx(s, sz+1, 0, 0) == sz) {
 			watch_junking(s);
-			s = (char *)rallocx(s, sz+1, 0);
+			s = (uint8_t *)rallocx(s, sz+1, 0);
 			assert_ptr_not_null((void *)s,
 			    "Unexpected rallocx() failure");
 			assert_true(!opt_junk_free || saw_junking,
diff --git a/test/unit/zero.c b/test/unit/zero.c
index 93afc2b8..30ebe37a 100644
--- a/test/unit/zero.c
+++ b/test/unit/zero.c
@@ -8,39 +8,41 @@ const char *malloc_conf =
 static void
 test_zero(size_t sz_min, size_t sz_max)
 {
-	char *s;
+	uint8_t *s;
 	size_t sz_prev, sz, i;
+#define	MAGIC	((uint8_t)0x61)
 
 	sz_prev = 0;
-	s = (char *)mallocx(sz_min, 0);
+	s = (uint8_t *)mallocx(sz_min, 0);
 	assert_ptr_not_null((void *)s, "Unexpected mallocx() failure");
 
 	for (sz = sallocx(s, 0); sz <= sz_max;
 	    sz_prev = sz, sz = sallocx(s, 0)) {
 		if (sz_prev > 0) {
-			assert_c_eq(s[0], 'a',
+			assert_u_eq(s[0], MAGIC,
 			    "Previously allocated byte %zu/%zu is corrupted",
 			    ZU(0), sz_prev);
-			assert_c_eq(s[sz_prev-1], 'a',
+			assert_u_eq(s[sz_prev-1], MAGIC,
 			    "Previously allocated byte %zu/%zu is corrupted",
 			    sz_prev-1, sz_prev);
 		}
 
 		for (i = sz_prev; i < sz; i++) {
-			assert_c_eq(s[i], 0x0,
+			assert_u_eq(s[i], 0x0,
 			    "Newly allocated byte %zu/%zu isn't zero-filled",
 			    i, sz);
-			s[i] = 'a';
+			s[i] = MAGIC;
 		}
 
 		if (xallocx(s, sz+1, 0, 0) == sz) {
-			s = (char *)rallocx(s, sz+1, 0);
+			s = (uint8_t *)rallocx(s, sz+1, 0);
 			assert_ptr_not_null((void *)s,
 			    "Unexpected rallocx() failure");
 		}
 	}
 
 	dallocx(s, 0);
+#undef MAGIC
 }
 
 TEST_BEGIN(test_zero_small)