diff --git a/riscemu/decoder/formats.py b/riscemu/decoder/formats.py
index 0b67d6a..296e6ca 100644
--- a/riscemu/decoder/formats.py
+++ b/riscemu/decoder/formats.py
@@ -55,12 +55,11 @@ def imm_u(ins: int):
 
 
 def imm_j(ins: int):
-    imm = ins >> 12
     return sign_extend(
-        ((imm >> 8) & 0b1111111111) +
-        ((imm & 1) << 10) +
-        ((imm & 0b11111111) << 11) +
-        (imm & 0b10000000000000000000), 20
+        (((ins >> 21) & 0b1111111111) << 1) +
+        (((ins >> 20) & 1) << 11) +
+        (((ins >> 12) & 0b11111111) << 12) +
+        (((ins >> 31) & 1) << 20), 21
     )