diff --git a/src/interfaces/libpq/win32.mak b/src/interfaces/libpq/win32.mak
index 1b71ebd3870..1d8c84d5a28 100644
--- a/src/interfaces/libpq/win32.mak
+++ b/src/interfaces/libpq/win32.mak
@@ -16,7 +16,7 @@ CPU=i386
 !MESSAGE Building the Win32 static library...
 !MESSAGE
 !ELSEIF ("$(CPU)" == "IA64")||("$(CPU)" == "AMD64")
-ADD_DEFINES=/D "WIN64" /Wp64 /GS
+ADD_DEFINES=/D "_WIN64" /Wp64 /GS
 ADD_SECLIB=bufferoverflowU.lib
 !MESSAGE Building the Win64 static library...
 !MESSAGE
diff --git a/src/test/regress/pg_regress.c b/src/test/regress/pg_regress.c
index 167444591df..2f6f56dd40f 100644
--- a/src/test/regress/pg_regress.c
+++ b/src/test/regress/pg_regress.c
@@ -2386,7 +2386,7 @@ regression_main(int argc, char *argv[], init_function ifunc, test_function tfunc
 
 		postmaster_running = true;
 
-#ifdef WIN64
+#ifdef _WIN64
 /* need a series of two casts to convert HANDLE without compiler warning */
 #define ULONGPID(x) (unsigned long) (unsigned long long) (x)
 #else