diff --git a/Changes b/Changes
index dbc9eb50d..d9e6ad37c 100644
--- a/Changes
+++ b/Changes
@@ -18,6 +18,7 @@ Verilator 5.039 devel
 * Add SPECIFYIGN warning for specify constructs that were previously silently ignored.
 * Add enum base data type, and wire data type checking per IEEE.
 * Add error on missing forward declarations (#6206). [Alex Solomatnikov]
+* Add `-DVERILATOR=1` definition to compiler flags when using verilated.mk.
 * Support member-level triggers for virtual interfaces (#5166) (#6148). [Yilou Wang]
 * Support randomization of scope variables with 'std::randomize()' (#5438) (#6185). [Yilou Wang]
 * Support disabling a fork in additional contexts (#5432 partial) (#6174) (#6183). [Ryszard Rozak, Antmicro Ltd.]
diff --git a/docs/guide/exe_verilator.rst b/docs/guide/exe_verilator.rst
index 3ed785b6d..1a1c3d802 100644
--- a/docs/guide/exe_verilator.rst
+++ b/docs/guide/exe_verilator.rst
@@ -32,7 +32,9 @@ Summary:
    makefile's VPATH the appropriate directory to find the file.
 
    See also :vlopt:`-CFLAGS` and :vlopt:`-LDFLAGS` options, which are
-   useful when the C++ files need special compiler flags.
+   useful when the C++ files need special compiler flags.  The compiler
+   flags add by default `-DVERILATOR=1`, so an `#ifdef VERILATOR` may be
+   used to conditionally preprocess .cpp code for different simulators.
 
 .. option:: <file.v>
 
diff --git a/include/verilated.mk.in b/include/verilated.mk.in
index a7a1f021c..fe1b081e1 100644
--- a/include/verilated.mk.in
+++ b/include/verilated.mk.in
@@ -84,6 +84,7 @@ VK_CPPFLAGS_ALWAYS += \
   -MMD \
   -I$(VERILATOR_ROOT)/include \
   -I$(VERILATOR_ROOT)/include/vltstd \
+  -DVERILATOR=1 \
   -DVM_COVERAGE=$(VM_COVERAGE) \
   -DVM_SC=$(VM_SC) \
   -DVM_TIMING=$(VM_TIMING) \
diff --git a/test_regress/Makefile_obj b/test_regress/Makefile_obj
index 81620d2f1..ac40f9146 100644
--- a/test_regress/Makefile_obj
+++ b/test_regress/Makefile_obj
@@ -22,9 +22,6 @@ VPATH += ../..
 
 #######################################################################
 
-# Needed by DPI tests
-CPPFLAGS += -DVERILATOR=1
-
 # Debugging
 CPPFLAGS += -DVL_DEBUG=1
 # Assertions disabled as SystemC libraries are not clean