diff --git a/litex/build/lattice/trellis.py b/litex/build/lattice/trellis.py
index b804df7a2..f4c7c05cf 100644
--- a/litex/build/lattice/trellis.py
+++ b/litex/build/lattice/trellis.py
@@ -28,6 +28,18 @@ nextpnr_ecp5_architectures = {
 }
 
 
+def nextpnr_ecp5_package(package):
+    if "285" in package:
+        return "CSFBGA285"
+    elif "381" in package:
+        return "CABGA381"
+    elif "554" in package:
+        return "CABGA554"
+    elif "756" in package:
+        return "CABGA756"
+    raise ValueError("Unknown package")
+
+
 def _format_constraint(c):
     if isinstance(c, Pins):
         return ("LOCATE COMP ", " SITE " + "\"" + c.identifiers[0] + "\"")
@@ -60,7 +72,7 @@ def _build_lpf(named_sc, named_pc):
 
 
 def _build_script(source, build_template, build_name, architecture,
-                  freq_constraint):
+                  package, freq_constraint):
     if sys.platform in ("win32", "cygwin"):
         script_ext = ".bat"
         build_script_contents = "@echo off\nrem Autogenerated by Migen\n\n"
@@ -74,6 +86,7 @@ def _build_script(source, build_template, build_name, architecture,
         s_fail = s + "{fail_stmt}\n"  # Required so Windows scripts fail early.
         build_script_contents += s_fail.format(build_name=build_name,
                                                architecture=architecture,
+                                               package=package,
                                                freq_constraint=freq_constraint,
                                                fail_stmt=fail_stmt)
 
@@ -129,7 +142,7 @@ class LatticeTrellisToolchain:
 
         self.build_template = [
             "yosys -q -l {build_name}.rpt {build_name}.ys",
-            "nextpnr-ecp5 --json {build_name}.json --lpf {build_name}.lpf --textcfg {build_name}.config --{architecture} --freq {freq_constraint}",
+            "nextpnr-ecp5 --json {build_name}.json --lpf {build_name}.lpf --textcfg {build_name}.config --{architecture} --package {package} --freq {freq_constraint}",
             "ecppack {build_name}.config {build_name}.bit"
         ]
 
@@ -168,11 +181,12 @@ class LatticeTrellisToolchain:
         # transform platform.device to nextpnr's architecture
         (family, size, package) = platform.device.split("-")
         architecture = nextpnr_ecp5_architectures[(family + "-" + size).lower()]
+        package = nextpnr_ecp5_package(package)
         freq_constraint = str(max(self.freq_constraints.values(),
                                   default=0.0))
 
         script = _build_script(False, self.build_template, build_name,
-                               architecture, freq_constraint)
+                               architecture, package, freq_constraint)
 
         # run scripts
         if run: