diff --git a/core/libs/prx/libkernel/System/src/Signals.cpp b/core/libs/prx/libkernel/System/src/Signals.cpp
index e6a955b74..dd7ad433c 100644
--- a/core/libs/prx/libkernel/System/src/Signals.cpp
+++ b/core/libs/prx/libkernel/System/src/Signals.cpp
@@ -53,7 +53,7 @@ void Dispatch(int native) {
     // Preserve the guest's persistent registration across CRT delivery.
     std::signal(native, Dispatch);
 #endif
-    if ((blockedMask.load() & (1u << guest)) != 0) return;
+    if ((blockedMask.load() & (1u << (guest - 1))) != 0) return;
     const auto callback = handlers[guest].load();
     if (reinterpret_cast<std::uintptr_t>(callback) > 1) callback(guest);
 }
diff --git a/core/libs/tests/GuestSignals.cpp b/core/libs/tests/GuestSignals.cpp
index 8c4548a81..dc5bf1a96 100644
--- a/core/libs/tests/GuestSignals.cpp
+++ b/core/libs/tests/GuestSignals.cpp
@@ -105,4 +105,16 @@ int main() {
         Require(sigaction_nid_postfix(fixed, &defaults, &current) == 0 && current.handler == 0);
     }
     Require(sigaction_nid_postfix(15, nullptr, nullptr) == 0);
+    Require(signal_nid_postfix(15, Callback) != invalid);
+    GuestSignalSet termMask{{1u << 14, 0, 0, 0}};
+    received = 0;
+    Require(sigprocmask_nid_postfix(1, &termMask, nullptr) == 0);
+    Require(raise_nid_postfix(15) == 0 && received == 0);
+    Require(sigprocmask_nid_postfix(2, &termMask, nullptr) == 0);
+    Require(raise_nid_postfix(15) == 0 && received == 15);
+    GuestSignalSet urgMask{{1u << 15, 0, 0, 0}};
+    received = 0;
+    Require(sigprocmask_nid_postfix(1, &urgMask, nullptr) == 0);
+    Require(raise_nid_postfix(15) == 0 && received == 15);
+    Require(sigprocmask_nid_postfix(2, &urgMask, nullptr) == 0);
 }