diff --git a/compiler-rt/test/builtins/Unit/atomic_test.c b/compiler-rt/test/builtins/Unit/atomic_test.c
--- a/compiler-rt/test/builtins/Unit/atomic_test.c
+++ b/compiler-rt/test/builtins/Unit/atomic_test.c
@@ -25,7 +25,7 @@
 // functions themselves, regardless of how the builtins are lowered. We need to
 // use asm labels because we can't redeclare the builtins.
 
-void __atomic_load_c(int size, const void *src, void *dest,
+void __atomic_load_c(int size, void *src, void *dest,
                      int model) asm("__atomic_load");
 
 uint8_t __atomic_load_1(uint8_t *src, int model);
@@ -177,16 +177,22 @@
 
     // Test with aligned data.
     for (int n = 1; n <= LEN(data); n++) {
+      // Note: __atomic_load requires a writable mapping, so we copy the data.
+      __attribute__((aligned(16))) char src[LEN(data)] = {0};
       __attribute__((aligned(16))) char dst[LEN(data)] = {0};
-      __atomic_load_c(n, data, dst, model);
+      memcpy(src, data, sizeof(src));
+      __atomic_load_c(n, src, dst, model);
       if (memcmp(dst, data, n) != 0)
         abort();
     }
 
     // Test with unaligned data.
     for (int n = 1; n < LEN(data); n++) {
+      // Note: __atomic_load requires a writable mapping, so we copy the data.
+      __attribute__((aligned(16))) char src[LEN(data)] = {0};
       __attribute__((aligned(16))) char dst[LEN(data)] = {0};
-      __atomic_load_c(n, data + 1, dst + 1, model);
+      memcpy(src, data, sizeof(src));
+      __atomic_load_c(n, src + 1, dst + 1, model);
       if (memcmp(dst + 1, data + 1, n) != 0)
         abort();
     }