diff --git a/libc/src/string/memory_utils/memcpy_utils.h b/libc/src/string/memory_utils/memcpy_utils.h
--- a/libc/src/string/memory_utils/memcpy_utils.h
+++ b/libc/src/string/memory_utils/memcpy_utils.h
@@ -90,7 +90,7 @@
   CopyBlock<kBlockSize>(dst, src); // Copy first block
 
   // Copy aligned blocks
-  const size_t ofla = offset_from_last_aligned<kBlockSize>(dst);
+  const size_t ofla = offset_from_last_aligned<kBlockSize>(src);
   const size_t limit = count + ofla - kBlockSize;
   for (size_t offset = kBlockSize; offset < limit; offset += kBlockSize)
     CopyBlock<kBlockSize>(dst - ofla + offset, src - ofla + offset);
diff --git a/libc/test/src/string/memory_utils/memcpy_utils_test.cpp b/libc/test/src/string/memory_utils/memcpy_utils_test.cpp
--- a/libc/test/src/string/memory_utils/memcpy_utils_test.cpp
+++ b/libc/test/src/string/memory_utils/memcpy_utils_test.cpp
@@ -162,14 +162,14 @@
 
 TEST(MemcpyUtilsTest, CopyAlignedBlocks) {
   auto &trace = GetTrace();
-  // Destination is aligned and multiple of alignment.
+  // Source is aligned and multiple of alignment.
   //   "1111"
   trace.Clear();
   CopyAlignedBlocks<4>(I(0), I(0), 4);
   EXPECT_STREQ(trace.Write(), "2222");
   EXPECT_STREQ(trace.Read(), "2222");
 
-  // Destination is aligned and multiple of alignment.
+  // Source is aligned and multiple of alignment.
   //   "11110000"
   // + "00001111"
   // = "11111111"
@@ -178,7 +178,7 @@
   EXPECT_STREQ(trace.Write(), "11111111");
   EXPECT_STREQ(trace.Read(), "11111111");
 
-  // Destination is aligned already overlap at end.
+  // Source is aligned already overlap at end.
   //   "1111000000000"
   // + "0000111100000"
   // + "0000000011110"
@@ -189,26 +189,26 @@
   EXPECT_STREQ(trace.Write(), "1111111112221");
   EXPECT_STREQ(trace.Read(), "1111111112221");
 
-  // Misaligned destination.
+  // Misaligned source.
   //   "01111000000000"
   // + "00001111000000"
   // + "00000000111100"
   // + "00000000001111"
   // = "01112111112211"
   trace.Clear();
-  CopyAlignedBlocks<4>(I(1), I(0), 13);
-  EXPECT_STREQ(trace.Write(), "01112111112211");
-  EXPECT_STREQ(trace.Read(), "1112111112211");
+  CopyAlignedBlocks<4>(I(0), I(1), 13);
+  EXPECT_STREQ(trace.Write(), "1112111112211");
+  EXPECT_STREQ(trace.Read(), "01112111112211");
 
-  // Misaligned destination aligned at end.
+  // Misaligned source aligned at end.
   //   "011110000000"
   // + "000011110000"
   // + "000000001111"
   // = "011121111111"
   trace.Clear();
-  CopyAlignedBlocks<4>(I(1), I(0), 11);
-  EXPECT_STREQ(trace.Write(), "011121111111");
-  EXPECT_STREQ(trace.Read(), "11121111111");
+  CopyAlignedBlocks<4>(I(0), I(1), 11);
+  EXPECT_STREQ(trace.Write(), "11121111111");
+  EXPECT_STREQ(trace.Read(), "011121111111");
 }
 
 TEST(MemcpyUtilsTest, MaxReloads) {