diff --git a/tests/buffer_tests.cpp b/tests/buffer_tests.cpp
index 7d830bb..a5a0c2a 100644
--- a/tests/buffer_tests.cpp
+++ b/tests/buffer_tests.cpp
@@ -381,15 +381,19 @@
   // Make the second page unreadable and unwritable.
   ASSERT_TRUE(mprotect(&memory[pagesize], pagesize, PROT_NONE) == 0);
 
-  uint8_t* dst = new uint8_t[pagesize];
-  for (size_t i = 0; i < pagesize; i++) {
-    uint8_t* src = &memory[pagesize-i];
+  uint8_t* dst_buffer = new uint8_t[2*pagesize];
+  // Change the dst alignment as we change the source.
+  for (size_t i = 0; i < 16; i++) {
+    uint8_t* dst = &dst_buffer[i];
+    for (size_t j = 0; j < pagesize; j++) {
+      uint8_t* src = &memory[pagesize-j];
 
-    test_func(src, dst, i);
+      test_func(src, dst, j);
+    }
   }
   ASSERT_TRUE(mprotect(&memory[pagesize], pagesize, PROT_READ | PROT_WRITE) == 0);
   free(memory);
-  delete[] dst;
+  delete[] dst_buffer;
 }
 
 void RunCmpBufferOverreadTest(
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index 80190d7..842e1c7 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -1174,7 +1174,7 @@
   return 1;
 }
 
-#define STRCAT_DST_LEN  128
+#define STRCAT_DST_LEN  64
 
 static void DoStrcatTest(uint8_t* src, uint8_t* dst, size_t len) {
   if (len >= 1) {
@@ -1189,7 +1189,7 @@
       int value2 = 32 + (value + 2) % 96;
       memset(cmp_buf, value2, sizeof(cmp_buf));
 
-      for (size_t i = 1; i <= STRCAT_DST_LEN; i++) {
+      for (size_t i = 1; i <= STRCAT_DST_LEN;) {
         memset(dst, value2, i-1);
         memset(dst+i-1, 0, len-i);
         src[len-i] = '\0';
@@ -1197,6 +1197,13 @@
                                                          reinterpret_cast<char*>(src))));
         ASSERT_TRUE(memcmp(dst, cmp_buf, i-1) == 0);
         ASSERT_TRUE(memcmp(src, dst+i-1, len-i+1) == 0);
+        // This is an expensive loop, so don't loop through every value,
+        // get to a certain size and then start doubling.
+        if (i < 16) {
+          i++;
+        } else {
+          i <<= 1;
+        }
       }
     } else {
       dst[0] = '\0';
@@ -1229,7 +1236,7 @@
       int value2 = 32 + (value + 2) % 96;
       memset(cmp_buf, value2, sizeof(cmp_buf));
 
-      for (size_t i = 1; i <= STRCAT_DST_LEN; i++) {
+      for (size_t i = 1; i <= STRCAT_DST_LEN;) {
         memset(dst, value2, i-1);
         memset(dst+i-1, 0, len-i);
         src[len-i] = '\0';
@@ -1237,6 +1244,13 @@
                                  reinterpret_cast<char*>(src), len));
         ASSERT_TRUE(memcmp(dst, cmp_buf, i-1) == 0);
         ASSERT_TRUE(memcmp(src, dst+i-1, len-i+1) == 0);
+        // This is an expensive loop, so don't loop through every value,
+        // get to a certain size and then start doubling.
+        if (i < 16) {
+          i++;
+        } else {
+          i <<= 1;
+        }
       }
     } else {
       dst[0] = '\0';