diff --git a/src/custom.zig b/src/custom.zig
index 0420bd3..a91bdd2 100644
--- a/src/custom.zig
+++ b/src/custom.zig
@@ -16,12 +16,15 @@ pub const RandomNoise = struct {
 
     pub fn init(
         allocator: *std.mem.Allocator,
-        params: var,
+        params: *plugins.ParamMap,
     ) ?RandomNoise {
-        var r = std.rand.DefaultPrng.init(params.seed);
+        const seed = @floatToInt(u64, params.get("seed").?.value);
+        const fillbytes = @floatToInt(usize, params.get("fill_bytes").?.value);
 
-        if (params.fill_bytes > 0) {
-            var rand_buf = allocator.alloc(f32, params.fill_bytes) catch return null;
+        var r = std.rand.DefaultPrng.init(seed);
+
+        if (fillbytes > 0) {
+            var rand_buf = allocator.alloc(f32, fillbytes) catch return null;
 
             for (rand_buf) |_, idx| {
                 rand_buf[idx] = r.random.float(f32);
@@ -64,12 +67,15 @@ pub const WildNoise = struct {
 
     pub fn init(
         allocator: *std.mem.Allocator,
-        params: var,
+        params: *plugins.ParamMap,
     ) ?WildNoise {
-        var r = std.rand.DefaultPrng.init(params.seed);
+        const seed = @floatToInt(u64, params.get("seed").?.value);
+        const fillbytes = @floatToInt(usize, params.get("fill_bytes").?.value);
 
-        if (params.fill_bytes > 0) {
-            var rand_buf = allocator.alloc(f32, params.fill_bytes) catch return null;
+        var r = std.rand.DefaultPrng.init(seed);
+
+        if (fillbytes > 0) {
+            var rand_buf = allocator.alloc(f32, fillbytes) catch return null;
 
             for (rand_buf) |_, idx| {
                 rand_buf[idx] = @intToFloat(f32, r.random.int(u1));
@@ -112,10 +118,10 @@ pub const Write = struct {
 
     pub fn init(
         allocator: *std.mem.Allocator,
-        params: var,
+        params: *plugins.ParamMap,
     ) Write {
         return Write{
-            .data = params.data,
+            .data = params.get("data").?.value,
         };
     }
 
@@ -133,10 +139,10 @@ pub const Embed = struct {
     sndfile: *c.SNDFILE = undefined,
     buf: []f32 = undefined,
 
-    pub fn init(allocator: *std.mem.Allocator, params: var) @This() {
+    pub fn init(allocator: *std.mem.Allocator, params: *plugins.ParmaMap) @This() {
         return Embed{
             .allocator = allocator,
-            .filepath = params.path,
+            .filepath = params.get("path").?.value,
         };
     }
 
diff --git a/src/image.zig b/src/image.zig
index b9202ef..d677afa 100644
--- a/src/image.zig
+++ b/src/image.zig
@@ -422,7 +422,7 @@ pub const Image = struct {
         self: *Image,
         comptime Plugin: type,
         position: plugins.Position,
-        extra: var,
+        extra: *ParamMap,
     ) !void {
         var plugin_opt: ?Plugin = Plugin.init(self.allocator, extra);
         if (plugin_opt == null) {
diff --git a/src/lang.zig b/src/lang.zig
index 3b7a542..cc8d58a 100644
--- a/src/lang.zig
+++ b/src/lang.zig
@@ -178,13 +178,13 @@ pub const Command = struct {
     };
 
     pub const Noise = CustomCommand(Tag.noise, custom.RandomNoise, struct {
-        seed: u64,
-        fill_bytes: usize,
+        seed: f32,
+        fill_bytes: f32,
     });
 
     pub const Wildnoise = CustomCommand(Tag.wildnoise, custom.WildNoise, struct {
-        seed: u64,
-        fill_bytes: usize,
+        seed: f32,
+        fill_bytes: f32,
     });
 
     pub const Write = CustomCommand(Tag.write, custom.Write, struct {
@@ -521,7 +521,7 @@ pub const Lang = struct {
         var cmd = try self.allocator.create(command_struct);
         const is_lv2_command = switch (command_struct.base_tag) {
             .noop, .load, .quicksave, .runqs, .rotate => false,
-            else => true,
+            else => command_struct.command_type == .lv2_command,
         };
 
         // TODO: crash when no arguments are left but we still need
@@ -543,6 +543,7 @@ pub const Lang = struct {
             cmd.split = try std.fmt.parseInt(usize, split.?, 10);
             cmd.index = try std.fmt.parseInt(usize, index.?, 10);
 
+            // All parameters for LV2 plugins are f32.
             inline for (@typeInfo(@TypeOf(cmd.parameters)).Struct.fields) |cmd_field| {
                 const maybe_arg = tok_it.next();
                 if (maybe_arg == null) {
@@ -551,15 +552,10 @@ pub const Lang = struct {
                 }
 
                 const arg = maybe_arg.?;
-                const arg_value = switch (cmd_field.field_type) {
-                    f32 => try std.fmt.parseFloat(f32, arg),
-                    u64 => try std.fmt.parseInt(u64, arg, 10),
-                    usize => try std.fmt.parseInt(usize, arg, 10),
-                    []const u8 => try self.allocator.dupe(u8, arg),
-                    else => @compileError("parameter struct has unsupported type " ++ @typeName(cmd_field.field_type)),
-                };
+                if (cmd_field.field_type != f32)
+                    @compileError("LV2 parameter struct can only have f32 fields");
 
-                @field(cmd.parameters, cmd_field.name) = arg_value;
+                @field(cmd.parameters, cmd_field.name) = try std.fmt.parseFloat(f32, arg);
             }
         } else {
             inline for (@typeInfo(command_struct).Struct.fields) |cmd_field| {
@@ -574,7 +570,7 @@ pub const Lang = struct {
                     i32 => try std.fmt.parseInt(i32, arg, 10),
                     f32 => try std.fmt.parseFloat(f32, arg),
                     []const u8 => try self.allocator.dupe(u8, arg),
-                    else => @compileError("Invalid parameter type (" ++ @typeName(cmd_field.field_type) ++ ") left on command struct " ++ @typeName(command_struct) ++ "."),
+                    else => @panic("Invalid parameter type (" ++ @typeName(cmd_field.field_type) ++ ") left on command struct " ++ @typeName(command_struct) ++ "."),
                 };
 
                 std.debug.warn("parsing {}, arg of type {} => {}\n", .{
diff --git a/src/runner.zig b/src/runner.zig
index dd5fcd2..db40493 100644
--- a/src/runner.zig
+++ b/src/runner.zig
@@ -230,8 +230,18 @@ pub const Runner = struct {
             .index = command.index,
         };
 
+        var params = ParamMap.init(self.allocator);
+        defer params.deinit();
+
+        inline for (@typeInfo(@TypeOf(command.parameters)).Struct.fields) |cmd_field| {
+            _ = try params.put(
+                cmd_field.name,
+                @field(command.parameters, cmd_field.name),
+            );
+        }
+
         var image = try self.getImage();
-        try image.runCustomPlugin(@TypeOf(command).plugin_type, pos, command.parameters);
+        try image.runCustomPlugin(@TypeOf(command).plugin_type, pos, &params);
     }
 
     fn newRunCommandSingle(