diff --git a/src/system/libroot/posix/malloc/heap.h b/src/system/libroot/posix/malloc/heap.h
index b2a9ed6ba3..f42962e2f2 100644
--- a/src/system/libroot/posix/malloc/heap.h
+++ b/src/system/libroot/posix/malloc/heap.h
@@ -74,8 +74,12 @@ class hoardHeap {
 #	error "Undefined size class base."
 #endif
 
-		// Every object is aligned so that it can always hold a double.
+		// Every object is aligned so that it can always hold any type.
+#ifdef __x86_64__
+		enum { ALIGNMENT = 16 };
+#else		
 		enum { ALIGNMENT = sizeof(double) };
+#endif
 
 		// ANDing with this rounds to ALIGNMENT.
 		enum { ALIGNMENT_MASK = ALIGNMENT - 1 };
diff --git a/src/tests/system/libroot/posix/Jamfile b/src/tests/system/libroot/posix/Jamfile
index 511752c30c..56396e89a1 100644
--- a/src/tests/system/libroot/posix/Jamfile
+++ b/src/tests/system/libroot/posix/Jamfile
@@ -16,7 +16,7 @@ SimpleTest flock_test : flock_test.cpp ;
 SimpleTest fseek_test : fseek_test.cpp ;
 SimpleTest getsubopt_test : getsubopt_test.cpp ;
 SimpleTest locale_test : locale_test.cpp ;
-SimpleTest memalign_test : memalign_test.cpp ;
+SimpleTest memalign_test : memalign_test.cpp : $(TARGET_LIBSUPC++) ;
 SimpleTest mprotect_test : mprotect_test.cpp ;
 SimpleTest pthread_signal_test : pthread_signal_test.cpp ;
 SimpleTest realtime_sem_test1 : realtime_sem_test1.cpp ;
diff --git a/src/tests/system/libroot/posix/memalign_test.cpp b/src/tests/system/libroot/posix/memalign_test.cpp
index 02b60bf99c..3908e05f24 100644
--- a/src/tests/system/libroot/posix/memalign_test.cpp
+++ b/src/tests/system/libroot/posix/memalign_test.cpp
@@ -53,7 +53,13 @@ allocate_random_no_alignment(int32 count, size_t maxSize)
 			printf("allocation of %lu bytes failed\n", sizes[i]);
 			exit(1);
 		}
-
+#ifdef __x86_64__
+		if (((addr_t)allocations[i] & 0xf) != 0) {
+			printf("allocation %p not aligned failed\n",
+				allocations[i]);
+			exit(1);
+		}
+#endif
 		write_test_pattern(allocations[i], sizes[i]);
 	}