diff --git a/mak/COPY b/mak/COPY
index 2de8a3c228..0e2265fc66 100644
--- a/mak/COPY
+++ b/mak/COPY
@@ -405,5 +405,6 @@ COPY=\
 	\
 	$(IMPDIR)\rt\array\comparison.d \
 	$(IMPDIR)\rt\array\equality.d \
+	$(IMPDIR)\rt\array\casting.d \
 	\
 	$(IMPDIR)\etc\linux\memoryerror.d
diff --git a/mak/SRCS b/mak/SRCS
index e068b323c1..23144ed002 100644
--- a/mak/SRCS
+++ b/mak/SRCS
@@ -453,6 +453,7 @@ SRCS=\
 	\
 	src\rt\array\comparison.d \
 	src\rt\array\equality.d \
+	src\rt\array\casting.d \
 	\
 	src\rt\backtrace\dwarf.d \
 	src\rt\backtrace\elf.d \
diff --git a/mak/WINDOWS b/mak/WINDOWS
index 276aa9e424..a1b75a356e 100644
--- a/mak/WINDOWS
+++ b/mak/WINDOWS
@@ -1193,3 +1193,6 @@ $(IMPDIR)\rt\array\comparison.d : src\rt\array\comparison.d
 
 $(IMPDIR)\rt\array\equality.d : src\rt\array\equality.d
 	copy $** $@
+
+$(IMPDIR)\rt\array\casting.d : src\rt\array\casting.d
+	copy $** $@
diff --git a/src/object.d b/src/object.d
index 97a8e5e9cd..f7850b0a8a 100644
--- a/src/object.d
+++ b/src/object.d
@@ -40,6 +40,7 @@ version (D_ObjectiveC) public import core.attribute : selector;
 
 public import rt.array.comparison : __cmp;
 public import rt.array.equality : __ArrayEq, __equals;
+public import rt.array.casting: __ArrayCast;
 
 // Compare class and interface objects for ordering.
 private int __cmp(Obj)(Obj lhs, Obj rhs)
@@ -4398,111 +4399,6 @@ void __ArrayDtor(T)(T[] a)
         e.__xdtor();
 }
 
-/**
-Used by `__ArrayCast` to emit a descriptive error message.
-
-It is a template so it can be used by `__ArrayCast` in -betterC
-builds.  It is separate from `__ArrayCast` to minimize code
-bloat.
-
-Params:
-    fromType = name of the type being cast from
-    fromSize = total size in bytes of the array being cast from
-    toType   = name of the type being cast o
-    toSize   = total size in bytes of the array being cast to
- */
-private void onArrayCastError()(string fromType, size_t fromSize, string toType, size_t toSize) @trusted
-{
-    import core.internal.string : unsignedToTempString;
-
-    const(char)[][9] msgComponents =
-    [
-        "An array of size "
-        , unsignedToTempString(fromSize)
-        , " does not align on an array of size "
-        , unsignedToTempString(toSize)
-        , ", so `"
-        , fromType
-        , "` cannot be cast to `"
-        , toType
-        , "`"
-    ];
-
-    // convert discontiguous `msgComponents` to contiguous string on the stack
-    enum msgLength = 2048;
-    char[msgLength] msg;
-
-    size_t index = 0;
-    foreach (m; msgComponents)
-    {
-        foreach (c; m)
-        {
-            msg[index++] = c;
-            if (index >= (msgLength - 1))
-                break;
-        }
-
-        if (index >= (msgLength - 1))
-            break;
-    }
-    msg[index] = '\0'; // null-termination
-
-    // first argument must evaluate to `false` at compile-time to maintain memory safety in release builds
-    assert(false, msg);
-}
-
-/**
-The compiler lowers expressions of `cast(TTo[])TFrom[]` to
-this implementation.
-
-Params:
-    from = the array to reinterpret-cast
-
-Returns:
-    `from` reinterpreted as `TTo[]`
- */
-TTo[] __ArrayCast(TFrom, TTo)(TFrom[] from) @nogc pure @trusted
-{
-    const fromSize = from.length * TFrom.sizeof;
-    const toLength = fromSize / TTo.sizeof;
-
-    if ((fromSize % TTo.sizeof) != 0)
-    {
-        onArrayCastError(TFrom.stringof, fromSize, TTo.stringof, toLength * TTo.sizeof);
-    }
-
-    struct Array
-    {
-        size_t length;
-        void* ptr;
-    }
-    auto a = cast(Array*)&from;
-    a.length = toLength; // jam new length
-    return *cast(TTo[]*)a;
-}
-
-@safe @nogc pure nothrow unittest
-{
-    byte[int.sizeof * 3] b = cast(byte) 0xab;
-    int[] i;
-    short[] s;
-
-    i = __ArrayCast!(byte, int)(b);
-    assert(i.length == 3);
-    foreach (v; i)
-        assert(v == cast(int) 0xabab_abab);
-
-    s = __ArrayCast!(byte, short)(b);
-    assert(s.length == 6);
-    foreach (v; s)
-        assert(v == cast(short) 0xabab);
-
-    s = __ArrayCast!(int, short)(i);
-    assert(s.length == 6);
-    foreach (v; s)
-        assert(v == cast(short) 0xabab);
-}
-
 // Allows customized assert error messages
 string _d_assert_fail(string comp, A, B)(A a, B b) @nogc @safe nothrow pure
 {
diff --git a/src/rt/array/casting.d b/src/rt/array/casting.d
new file mode 100644
index 0000000000..d8ca79af2d
--- /dev/null
+++ b/src/rt/array/casting.d
@@ -0,0 +1,115 @@
+/**
+ This module contains compiler support for casting dynamic arrays
+
+  Copyright: Copyright Digital Mars 2000 - 2019.
+  License: Distributed under the
+       $(LINK2 http://www.boost.org/LICENSE_1_0.txt, Boost Software License 1.0).
+     (See accompanying file LICENSE)
+  Source: $(DRUNTIMESRC rt/_array/_casting.d)
+*/
+module rt.array.casting;
+
+/**
+Used by `__ArrayCast` to emit a descriptive error message.
+
+It is a template so it can be used by `__ArrayCast` in -betterC
+builds.  It is separate from `__ArrayCast` to minimize code
+bloat.
+
+Params:
+    fromType = name of the type being cast from
+    fromSize = total size in bytes of the array being cast from
+    toType   = name of the type being cast o
+    toSize   = total size in bytes of the array being cast to
+ */
+private void onArrayCastError()(string fromType, size_t fromSize, string toType, size_t toSize) @trusted
+{
+    import core.internal.string : unsignedToTempString;
+
+    const(char)[][9] msgComponents =
+    [
+        "An array of size "
+        , unsignedToTempString(fromSize)
+        , " does not align on an array of size "
+        , unsignedToTempString(toSize)
+        , ", so `"
+        , fromType
+        , "` cannot be cast to `"
+        , toType
+        , "`"
+    ];
+
+    // convert discontiguous `msgComponents` to contiguous string on the stack
+    enum msgLength = 2048;
+    char[msgLength] msg;
+
+    size_t index = 0;
+    foreach (m; msgComponents)
+    {
+        foreach (c; m)
+        {
+            msg[index++] = c;
+            if (index >= (msgLength - 1))
+                break;
+        }
+
+        if (index >= (msgLength - 1))
+            break;
+    }
+    msg[index] = '\0'; // null-termination
+
+    // first argument must evaluate to `false` at compile-time to maintain memory safety in release builds
+    assert(false, msg);
+}
+
+/**
+The compiler lowers expressions of `cast(TTo[])TFrom[]` to
+this implementation.
+
+Params:
+    from = the array to reinterpret-cast
+
+Returns:
+    `from` reinterpreted as `TTo[]`
+ */
+TTo[] __ArrayCast(TFrom, TTo)(TFrom[] from) @nogc pure @trusted
+{
+    const fromSize = from.length * TFrom.sizeof;
+    const toLength = fromSize / TTo.sizeof;
+
+    if ((fromSize % TTo.sizeof) != 0)
+    {
+        onArrayCastError(TFrom.stringof, fromSize, TTo.stringof, toLength * TTo.sizeof);
+    }
+
+    struct Array
+    {
+        size_t length;
+        void* ptr;
+    }
+    auto a = cast(Array*)&from;
+    a.length = toLength; // jam new length
+    return *cast(TTo[]*)a;
+}
+
+@safe @nogc pure nothrow unittest
+{
+    byte[int.sizeof * 3] b = cast(byte) 0xab;
+    int[] i;
+    short[] s;
+
+    i = __ArrayCast!(byte, int)(b);
+    assert(i.length == 3);
+    foreach (v; i)
+        assert(v == cast(int) 0xabab_abab);
+
+    s = __ArrayCast!(byte, short)(b);
+    assert(s.length == 6);
+    foreach (v; s)
+        assert(v == cast(short) 0xabab);
+
+    s = __ArrayCast!(int, short)(i);
+    assert(s.length == 6);
+    foreach (v; s)
+        assert(v == cast(short) 0xabab);
+}