diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -16020,16 +16020,22 @@
     llvm::APInt size = ArrayTy->getSize();
 
     if (BaseType != EffectiveType) {
-      // Make sure we're comparing apples to apples when comparing index to size
+      // Make sure we're comparing apples to apples when comparing index to
+      // size.
       uint64_t ptrarith_typesize = Context.getTypeSize(EffectiveType);
       uint64_t array_typesize = Context.getTypeSize(BaseType);
-      // Handle ptrarith_typesize being zero, such as when casting to void*
-      if (!ptrarith_typesize) ptrarith_typesize = 1;
+
+      // Handle ptrarith_typesize being zero, such as when casting to void*.
+      // Use the size in bits (what "getTypeSize()" returns) rather than bytes.
+      if (!ptrarith_typesize)
+        ptrarith_typesize = Context.getCharWidth();
+
       if (ptrarith_typesize != array_typesize) {
-        // There's a cast to a different size type involved
+        // There's a cast to a different size type involved.
         uint64_t ratio = array_typesize / ptrarith_typesize;
+
         // TODO: Be smarter about handling cases where array_typesize is not a
-        // multiple of ptrarith_typesize
+        // multiple of ptrarith_typesize.
         if (ptrarith_typesize * ratio == array_typesize)
           size *= llvm::APInt(size.getBitWidth(), ratio);
       }
diff --git a/clang/test/Sema/array-bounds-ptr-arith.c b/clang/test/Sema/array-bounds-ptr-arith.c
--- a/clang/test/Sema/array-bounds-ptr-arith.c
+++ b/clang/test/Sema/array-bounds-ptr-arith.c
@@ -6,13 +6,12 @@
 struct ext2_super_block{
   unsigned char s_uuid[8]; // expected-note {{declared here}}
 };
-void* ext2_statfs (struct ext2_super_block *es,int a)
-{
-	 return (void *)es->s_uuid + sizeof(int); // no-warning
+
+void* ext2_statfs (struct ext2_super_block *es,int a) {
+  return (void *)es->s_uuid + sizeof(int); // no-warning
 }
-void* broken (struct ext2_super_block *es,int a)
-{
-	 return (void *)es->s_uuid + 80; // expected-warning {{refers past the end of the array}}
+void* broken (struct ext2_super_block *es,int a) {
+  return (void *)es->s_uuid + 9; // expected-warning {{the pointer incremented by 9 refers past the end of the array}}
 }
 
 // Test case reduced from PR11594