diff --git a/include/libremidi/backends/linux/pipewire/context.hpp b/include/libremidi/backends/linux/pipewire/context.hpp
index dfdeec63..a983d0a5 100644
--- a/include/libremidi/backends/linux/pipewire/context.hpp
+++ b/include/libremidi/backends/linux/pipewire/context.hpp
@@ -308,7 +308,13 @@ class context : public std::enable_shared_from_this<context>
         }
         return 0;
       };
-      pw_loop_invoke(m_loop, trampoline, 0, nullptr, 0, /*block=*/true, &f);
+      // A blocking pw_loop_invoke from a foreign thread fires the loop
+      // control hooks (thread-loop unlock before the wait / lock after),
+      // which REQUIRE the caller to hold the thread-loop lock. Calling
+      // without it underflows the recurse counter (refused unlock) and
+      // then acquires the mutex on the way out, deadlocking the loop.
+      with_lock(
+          [&] { pw_loop_invoke(m_loop, trampoline, 0, nullptr, 0, /*block=*/true, &f); });
     }
     else
     {
@@ -330,7 +336,9 @@ class context : public std::enable_shared_from_this<context>
         }
         return 0;
       };
-      pw_loop_invoke(m_loop, trampoline, 0, nullptr, 0, /*block=*/true, &p);
+      // See the void branch: blocking invokes require the thread-loop lock.
+      with_lock(
+          [&] { pw_loop_invoke(m_loop, trampoline, 0, nullptr, 0, /*block=*/true, &p); });
       return std::move(*p.result);
     }
   }
diff --git a/include/libremidi/backends/linux/pipewire/format.hpp b/include/libremidi/backends/linux/pipewire/format.hpp
index d83c7eb3..6d11780c 100644
--- a/include/libremidi/backends/linux/pipewire/format.hpp
+++ b/include/libremidi/backends/linux/pipewire/format.hpp
@@ -320,10 +320,15 @@ inline const spa_pod* format_negotiation::build_buffers_param(
       data_type = (1u << SPA_DATA_MemPtr);
       break;
   }
+  // size/stride are RANGES with our tight computation as the minimum:
+  // producers commonly deliver row-padded buffers (GPU-allocated strides),
+  // and a fixed Int here fails the param intersection against any producer
+  // whose size differs — killing the link instead of accepting padding.
   return reinterpret_cast<const spa_pod*>(spa_pod_builder_add_object(
       &builder, SPA_TYPE_OBJECT_ParamBuffers, SPA_PARAM_Buffers, SPA_PARAM_BUFFERS_buffers,
       SPA_POD_CHOICE_RANGE_Int(8, 2, 16), SPA_PARAM_BUFFERS_blocks, SPA_POD_Int(blocks),
-      SPA_PARAM_BUFFERS_size, SPA_POD_Int(size), SPA_PARAM_BUFFERS_stride, SPA_POD_Int(stride),
+      SPA_PARAM_BUFFERS_size, SPA_POD_CHOICE_RANGE_Int(size, size, INT32_MAX),
+      SPA_PARAM_BUFFERS_stride, SPA_POD_CHOICE_RANGE_Int(stride, stride, INT32_MAX),
       SPA_PARAM_BUFFERS_dataType, SPA_POD_CHOICE_FLAGS_Int(data_type)));
 }