diff --git a/bronzebeard/asm.py b/bronzebeard/asm.py
index 6269e45..b3feb79 100644
--- a/bronzebeard/asm.py
+++ b/bronzebeard/asm.py
@@ -751,6 +751,8 @@ def cj_type(imm, *, opcode, funct3, cs=None):
 FENCE      = partial(fence,    opcode=0b0001111, funct3=0b000, rd=0, rs1=0, fm=0)  # special syntax*
 ECALL      = partial(i_type,   opcode=0b1110011, funct3=0b000, rd=0, rs1=0, imm=0)  # special syntax
 EBREAK     = partial(i_type,   opcode=0b1110011, funct3=0b000, rd=0, rs1=0, imm=1)  # special syntax
+MRET       = partial(i_type,   opcode=0b1110011, funct3=0b000, rd=0, rs1=0, imm=0b001100000010)  # special syntax
+WFI        = partial(i_type,   opcode=0b1110011, funct3=0b000, rd=0, rs1=0, imm=0b000100000101)  # special syntax
 
 # RV32/RV64 "Zifencei" Instruction-Fetch Fence
 FENCE_I    = partial(i_type,   opcode=0b0001111, funct3=0b001, rd=0, rs1=0, imm=0)  # special syntax
@@ -864,6 +866,8 @@ def cj_type(imm, *, opcode, funct3, cs=None):
 IE_TYPE_INSTRUCTIONS = {
     'ecall':      ECALL,
     'ebreak':     EBREAK,
+    'mret':       MRET,
+    'wfi':        WFI,
     'fence.i':    FENCE_I,
 }
 
@@ -2460,16 +2464,29 @@ def parse_item(line_tokens):
         return CATypeInstruction(line, name, rd_rs1, rs2)
     # cb-type instructions
     elif head in CB_TYPE_INSTRUCTIONS:
-        name, rs1, *imm = tokens
+        if len(tokens) != 3:
+            raise AssemblerError('cb-type instructions require exactly 3 args', line)
+        name, rs1, reference = tokens
         name = name.lower()
+        if is_int(reference):
+            imm = [reference]
+        else:
+            imm = ['%offset', reference]
         imm = parse_immediate(imm, line)
         return CBTypeInstruction(line, name, rs1, imm)
     # cj-type instructions
     elif head in CJ_TYPE_INSTRUCTIONS:
-        name, *imm = tokens
+        if len(tokens) != 2:
+            raise AssemblerError('cj-type instructions require exactly 2 args', line)
+        name, reference = tokens
         name = name.lower()
+        if is_int(reference):
+            imm = [reference]
+        else:
+            imm = ['%offset', reference]
         imm = parse_immediate(imm, line)
         return CJTypeInstruction(line, name, imm)
+
     # pseudo instructions
     elif head in PSEUDO_INSTRUCTIONS:
         name, *args = tokens
diff --git a/docs/instruction_reference.rst b/docs/instruction_reference.rst
index 0019fa3..bf19ab5 100644
--- a/docs/instruction_reference.rst
+++ b/docs/instruction_reference.rst
@@ -124,6 +124,8 @@ Instruction                  Description
 :code:`fence succ, pred`     order device I/O and memory accesses
 :code:`ecall`                make a service request to the execution environment
 :code:`ebreak`               return control to a debugging environment
+:code:`mret`                 return execution from a trap
+:code:`wfi`                  wait for interrupt
 ===========================  ===========
 
 RV32M Standard Extension
diff --git a/tests/test_isa_base_i.py b/tests/test_isa_base_i.py
index e4ad1ae..24908bc 100644
--- a/tests/test_isa_base_i.py
+++ b/tests/test_isa_base_i.py
@@ -574,10 +574,14 @@ def test_fence(succ, pred, code):
 def test_ecall():
     assert asm.ECALL() == 0b00000000000000000000000001110011
 
-
 def test_ebreak():
     assert asm.EBREAK() == 0b00000000000100000000000001110011
 
+def test_wfi():
+    assert asm.WFI() == 0b0001000_00101_0000000000000_1110011
+
+def test_mret():
+    assert asm.MRET() == 0b0011000_00010_0000000000000_1110011
 
 @pytest.mark.parametrize(
     'source,           expected', [