diff --git a/generator/spirv/generator.zig b/generator/spirv/generator.zig
index 70b454a..483a02c 100644
--- a/generator/spirv/generator.zig
+++ b/generator/spirv/generator.zig
@@ -6,9 +6,30 @@ pub fn generate(allocator: *Allocator, spec_jsons: []const []const u8, writer: a
     var arena = std.heap.ArenaAllocator.init(allocator);
     defer arena.deinit();
 
-    const registries = try arena.allocator.alloc(reg.Registry, spec_jsons.len);
-    for (registries) |*registry, i| {
-        var tokens = std.json.TokenStream.init(spec_jsons[i]);
-        registry.* = try std.json.parse(reg.Registry, &tokens, .{.allocator = &arena.allocator});
+    // Only one of the passed specs may be core (and one of them _must_ be core) -
+    // the others must be exensions.
+    var core_registry: reg.CoreRegistry = undefined;
+    const num_ext_registries = spec_jsons.len - 1;
+    const ext_registries = try arena.allocator.alloc(reg.ExtensionRegistry, num_ext_registries);
+
+    var ext_registry_i: usize = 0;
+    for (spec_jsons) |spec_json| {
+        var tokens = std.json.TokenStream.init(spec_json);
+        const registry = try std.json.parse(reg.Registry, &tokens, .{.allocator = &arena.allocator});
+        switch (registry) {
+            .core => |parsed_core_registry| core_registry = parsed_core_registry,
+            .extension => |parsed_ext_registry| {
+                if (ext_registry_i == num_ext_registries) {
+                    return error.NoCoreRegistry;
+                }
+
+                ext_registries[ext_registry_i] = parsed_ext_registry;
+                ext_registry_i += 1;
+            },
+        }
+    }
+
+    if (ext_registry_i != num_ext_registries) {
+        return error.MultipleCoreRegistries;
     }
 }
diff --git a/generator/spirv/registry.zig b/generator/spirv/registry.zig
index 60a1be7..4f89f07 100644
--- a/generator/spirv/registry.zig
+++ b/generator/spirv/registry.zig
@@ -18,10 +18,9 @@ pub const CoreRegistry = struct {
 pub const ExtensionRegistry = struct {
     copyright: [][]const u8,
     version: u32,
-    minor_version: u32,
     revision: u32,
     instructions: []Instruction,
-    operand_kinds: []OperandKind,
+    operand_kinds: []OperandKind = &[_]OperandKind{},
 };
 
 pub const Instruction = struct {