diff --git a/riscv_config/constants.py b/riscv_config/constants.py
index 2913757..4b9c583 100644
--- a/riscv_config/constants.py
+++ b/riscv_config/constants.py
@@ -21,10 +21,10 @@
 ] + Zvef_extensions + Zved_extensions
 
 Z_extensions = [
-        "Zicbom", "Zicbop", "Zicboz", "Zicntr", "Zicsr", "Zicond", "Zicfilp", "Zicfiss", "Zifencei", "Zihintpause", "Zihpm", "Zimop",
+        "Zicbom", "Zicbop", "Zicboz", "Zicntr", "Zicsr", "Zicond", "Zicfilp", "Zicfiss", "Zifencei", "Zihintpause", "Zihpm", "Zilsd", "Zimop",
         "Zmmul",
         "Zam", "Zabha", "Zacas",
-        "Zca", "Zcb", "Zcf", "Zcd" , "Zcmp", "Zcmt", "Zcmop", 
+        "Zca", "Zcb", "Zcf", "Zcd" , "Zcmp", "Zcmt", "Zcmop", "Zcmlsd",
         "Zfh", "Zfa",
         "Zfinx", "Zdinx", "Zhinx", "Zhinxmin",
         "Ztso",
diff --git a/riscv_config/isa_validator.py b/riscv_config/isa_validator.py
index 94f7412..c71ad89 100644
--- a/riscv_config/isa_validator.py
+++ b/riscv_config/isa_validator.py
@@ -82,6 +82,12 @@ def get_extension_list(isa):
     if 'S' in extension_list and not 'U' in extension_list:
         err_list.append( "S cannot exist without U.")
         err = True
+    if 'Zcmlsd' in extension_list and 'Zcf' in extension_list:
+        err_list.append( "Zcmlsd encodings are mutually exclusive with Zcf.")
+        err = True
+    if 'Zcmlsd' in extension_list and 'Zilsd' not in extension_list:
+        err_list.append( "Zcmlsd cannot exist without Zilsd.")
+        err = True
     if 'Zkn' in extension_list and ( set(['Zbkb', 'Zbkc', 'Zbkx', 'Zkne', 'Zknd', 'Zknh']) & set(extension_list)):
         err_list.append( "Zkn is a superset of Zbkb, Zbkc, Zbkx, Zkne, Zknd, Zknh. In presence of Zkn the subsets must be ignored in the ISA string.")
         err = True