diff --git a/ice40/bitstream.cc b/ice40/bitstream.cc
index b0f6260d..1b6a9425 100644
--- a/ice40/bitstream.cc
+++ b/ice40/bitstream.cc
@@ -227,7 +227,7 @@ void write_asc(const Context *ctx, std::ostream &out)
         out << ".device 5k" << std::endl;
         break;
     default:
-        NPNR_ASSERT_FALSE("unsupported device type");
+        NPNR_ASSERT_FALSE("unsupported device type\n");
     }
     // Set pips
     for (auto pip : ctx->getPips()) {
@@ -561,10 +561,10 @@ void read_config(Context *ctx, std::istream &in, chipconfig_t &config)
                     expected = "5k";
                     break;
                 default:
-                    log_error("unsupported device type");
+                    log_error("unsupported device type\n");
                 }
                 if (expected != config_device)
-                    log_error("device type does not match");
+                    log_error("device type does not match\n");
             } else if (!strcmp(tok, ".io_tile") || !strcmp(tok, ".logic_tile") || !strcmp(tok, ".ramb_tile") ||
                        !strcmp(tok, ".ramt_tile") || !strcmp(tok, ".ipcon_tile") || !strcmp(tok, ".dsp0_tile") ||
                        !strcmp(tok, ".dsp1_tile") || !strcmp(tok, ".dsp2_tile") || !strcmp(tok, ".dsp3_tile")) {
@@ -574,7 +574,7 @@ void read_config(Context *ctx, std::istream &in, chipconfig_t &config)
 
                 TileType tile = tile_at(ctx, tile_x, tile_y);
                 if (tok != tagTileType(tile))
-                    log_error("Wrong tile type for specified position");
+                    log_error("Wrong tile type for specified position\n");
 
             } else if (!strcmp(tok, ".extra_bit")) {
                 /*
diff --git a/ice40/main.cc b/ice40/main.cc
index c14b6086..652196a1 100644
--- a/ice40/main.cc
+++ b/ice40/main.cc
@@ -66,6 +66,12 @@ void svg_dump_decal(const Context *ctx, const DecalXY &decal)
     }
 }
 
+void conflicting_options(const boost::program_options::variables_map &vm, const char *opt1, const char *opt2)
+{
+    if (vm.count(opt1) && !vm[opt1].defaulted() && vm.count(opt2) && !vm[opt2].defaulted())
+        log_error((std::string("Conflicting options '") + opt1 + "' and '" + opt2 + "'.").c_str());
+}
+
 int main(int argc, char *argv[])
 {
     try {
@@ -122,13 +128,17 @@ int main(int argc, char *argv[])
             po::store(parsed, vm);
 
             po::notify(vm);
-        }
-
-        catch (std::exception &e) {
+        } catch (std::exception &e) {
             std::cout << e.what() << "\n";
             return 1;
         }
 
+        conflicting_options(vm, "read", "json");
+#ifndef ICE40_HX1K_ONLY
+        if ((vm.count("lp384") + vm.count("lp1k") + vm.count("lp8k") + vm.count("hx1k") + vm.count("hx8k") +
+             vm.count("up5k")) > 1)
+            log_error("Only one device type can be set\n");
+#endif
         if (vm.count("help") || argc == 1) {
         help:
             std::cout << boost::filesystem::basename(argv[0])