diff --git a/docs/ispc.txt b/docs/ispc.txt
index d682f6d1..d8adace4 100644
--- a/docs/ispc.txt
+++ b/docs/ispc.txt
@@ -471,6 +471,9 @@ preprocessor runs:
   * - ISPC_TARGET_{SSE2,SSE4,AVX}
     - 1
     - One of these will be set, depending on the compilation target.
+  * - ISPC_POINTER_SIZE
+    - 32 or 64
+    - Number of bits used to represent a pointer for the target architecture.
   * - ISPC_MAJOR_VERSION
     - 1
     - Major version of the ``ispc`` compiler/language
diff --git a/module.cpp b/module.cpp
index bfc55381..80aec28b 100644
--- a/module.cpp
+++ b/module.cpp
@@ -1176,6 +1176,11 @@ Module::execPreprocessor(const char* infilename, llvm::raw_string_ostream* ostre
         FATAL("Unhandled target ISA in preprocessor symbol definition");
     }
 
+    if (g->target.is32Bit)
+        opts.addMacroDef("ISPC_POINTER_SIZE=32");
+    else
+        opts.addMacroDef("ISPC_POINTER_SIZE=64");
+
     opts.addMacroDef("ISPC_MAJOR_VERSION=1");
     opts.addMacroDef("ISPC_MINOR_VERSION=1");