diff --git a/nmake.opt b/nmake.opt
index bd5719c2d1..f6101ccd59 100644
--- a/nmake.opt
+++ b/nmake.opt
@@ -127,18 +127,28 @@ CXX_PDB_FLAGS=/Zi /Fd$(GDAL_ROOT)\gdal$(VERSION).pdb
 CXX_PDB_FLAGS=
 !ENDIF
 
+# Flags to choose CRT variant to link against (e.g. static: /MT, /MTd, dynamic: /MD, /MDd)
+# Ensure MRSID_CONFIG in mrsid/nmake.opt is set appropriately as well
+!IFNDEF CXX_CRT_FLAGS
+!IFNDEF DEBUG
+CXX_CRT_FLAGS=/MD
+!ELSE
+CXX_CRT_FLAGS=/MDd
+!ENDIF
+!ENDIF
+
 !IFNDEF OPTFLAGS
 !IF $(MSVC_VER) >= 1400
 !IFNDEF DEBUG
-OPTFLAGS= $(CXX_ANALYZE_FLAGS) $(CXX_PDB_FLAGS) /nologo /MP /MD /EHsc /Ox /FC /D_CRT_SECURE_NO_DEPRECATE /D_CRT_NONSTDC_NO_DEPRECATE /DNDEBUG
+OPTFLAGS= $(CXX_ANALYZE_FLAGS) $(CXX_PDB_FLAGS) /nologo $(CXX_CRT_FLAGS) /EHsc /Ox /D_CRT_SECURE_NO_DEPRECATE /D_CRT_NONSTDC_NO_DEPRECATE /DNDEBUG
 !ELSE
-OPTFLAGS= $(CXX_ANALYZE_FLAGS) $(CXX_PDB_FLAGS) /nologo /MP /MD /EHsc /FC /D_CRT_SECURE_NO_DEPRECATE /D_CRT_NONSTDC_NO_DEPRECATE /DDEBUG
+OPTFLAGS= $(CXX_ANALYZE_FLAGS) $(CXX_PDB_FLAGS) /nologo $(CXX_CRT_FLAGS) /EHsc /D_CRT_SECURE_NO_DEPRECATE /D_CRT_NONSTDC_NO_DEPRECATE /DDEBUG
 !ENDIF
 !ELSE
 !IFNDEF DEBUG
-OPTFLAGS= $(CXX_PDB_FLAGS) /nologo /MD /EHsc /GR /Ox /FC /DNDEBUG
+OPTFLAGS= $(CXX_PDB_FLAGS) /nologo $(CXX_CRT_FLAGS) /EHsc /GR /Ox /DNDEBUG
 !ELSE
-OPTFLAGS= $(CXX_PDB_FLAGS) /nologo /MD /EHsc /GR /FC /DDEBUG
+OPTFLAGS= $(CXX_PDB_FLAGS) /nologo $(CXX_CRT_FLAGS) /EHsc /GR /DDEBUG
 !ENDIF
 !ENDIF  #MSVC_VER
 !ENDIF  # OPTFLAGS