diff --git a/src/tint/reader/spirv/function.cc b/src/tint/reader/spirv/function.cc
index e133e585cc..58941ebc45 100644
--- a/src/tint/reader/spirv/function.cc
+++ b/src/tint/reader/spirv/function.cc
@@ -327,6 +327,8 @@ std::string GetGlslStd450FuncName(uint32_t ext_opcode) {
             return "exp2";
         case GLSLstd450FaceForward:
             return "faceForward";
+        case GLSLstd450FindILsb:
+            return "firstTrailingBit";
         case GLSLstd450Floor:
             return "floor";
         case GLSLstd450Fma:
@@ -427,7 +429,6 @@ std::string GetGlslStd450FuncName(uint32_t ext_opcode) {
         case GLSLstd450PackDouble2x32:
         case GLSLstd450UnpackDouble2x32:
 
-        case GLSLstd450FindILsb:
         case GLSLstd450FindSMsb:
         case GLSLstd450FindUMsb:
 
diff --git a/src/tint/reader/spirv/function_glsl_std_450_test.cc b/src/tint/reader/spirv/function_glsl_std_450_test.cc
index c5131e9ac2..7a4fd94394 100644
--- a/src/tint/reader/spirv/function_glsl_std_450_test.cc
+++ b/src/tint/reader/spirv/function_glsl_std_450_test.cc
@@ -179,6 +179,8 @@ using SpvParserTest_GlslStd450_Inting_IntingInting =
     SpvParserTestBase<::testing::TestWithParam<GlslStd450Case>>;
 using SpvParserTest_GlslStd450_Inting_IntingIntingInting =
     SpvParserTestBase<::testing::TestWithParam<GlslStd450Case>>;
+using SpvParserTest_GlslStd450_Uinting_Uinting =
+    SpvParserTestBase<::testing::TestWithParam<GlslStd450Case>>;
 using SpvParserTest_GlslStd450_Uinting_UintingUinting =
     SpvParserTestBase<::testing::TestWithParam<GlslStd450Case>>;
 using SpvParserTest_GlslStd450_Uinting_UintingUintingUinting =
@@ -580,7 +582,8 @@ TEST_P(SpvParserTest_GlslStd450_Inting_IntingIntingInting, Vector) {
 
 INSTANTIATE_TEST_SUITE_P(Samples,
                          SpvParserTest_GlslStd450_Inting_Inting,
-                         ::testing::Values(GlslStd450Case{"SAbs", "abs"}));
+                         ::testing::Values(GlslStd450Case{"SAbs", "abs"},
+                                           GlslStd450Case{"FindILsb", "firstTrailingBit"}));
 
 INSTANTIATE_TEST_SUITE_P(Samples,
                          SpvParserTest_GlslStd450_Inting_IntingInting,
@@ -591,6 +594,41 @@ INSTANTIATE_TEST_SUITE_P(Samples,
                          SpvParserTest_GlslStd450_Inting_IntingIntingInting,
                          ::testing::Values(GlslStd450Case{"SClamp", "clamp"}));
 
+TEST_P(SpvParserTest_GlslStd450_Uinting_Uinting, Scalar) {
+    const auto assembly = Preamble() + R"(
+     %1 = OpExtInst %uint %glsl )" +
+                          GetParam().opcode +
+                          R"( %u1
+     OpReturn
+     OpFunctionEnd
+  )";
+    auto p = parser(test::Assemble(assembly));
+    ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions()) << assembly;
+    auto fe = p->function_emitter(100);
+    EXPECT_TRUE(fe.EmitBody()) << p->error();
+    auto ast_body = fe.ast_body();
+    const auto body = test::ToString(p->program(), ast_body);
+    EXPECT_THAT(body, HasSubstr("let x_1 : u32 = " + GetParam().wgsl_func + "(u1);")) << body;
+}
+
+TEST_P(SpvParserTest_GlslStd450_Uinting_Uinting, Vector) {
+    const auto assembly = Preamble() + R"(
+     %1 = OpExtInst %v2uint %glsl )" +
+                          GetParam().opcode +
+                          R"( %v2u1
+     OpReturn
+     OpFunctionEnd
+  )";
+    auto p = parser(test::Assemble(assembly));
+    ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+    auto fe = p->function_emitter(100);
+    EXPECT_TRUE(fe.EmitBody()) << p->error();
+    auto ast_body = fe.ast_body();
+    const auto body = test::ToString(p->program(), ast_body);
+    EXPECT_THAT(body, HasSubstr("let x_1 : vec2<u32> = " + GetParam().wgsl_func + "(v2u1);"))
+        << body;
+}
+
 TEST_P(SpvParserTest_GlslStd450_Uinting_UintingUinting, Scalar) {
     const auto assembly = Preamble() + R"(
      %1 = OpExtInst %uint %glsl )" +
@@ -661,6 +699,10 @@ TEST_P(SpvParserTest_GlslStd450_Uinting_UintingUintingUinting, Vector) {
         << body;
 }
 
+INSTANTIATE_TEST_SUITE_P(Samples,
+                         SpvParserTest_GlslStd450_Uinting_Uinting,
+                         ::testing::Values(GlslStd450Case{"FindILsb", "firstTrailingBit"}));
+
 INSTANTIATE_TEST_SUITE_P(Samples,
                          SpvParserTest_GlslStd450_Uinting_UintingUinting,
                          ::testing::Values(GlslStd450Case{"UMax", "max"},
@@ -907,6 +949,34 @@ TEST_F(SpvParserTest, RectifyOperandsAndResult_UClamp) {
         << body;
 }
 
+TEST_F(SpvParserTest, RectifyOperandsAndResult_FindILsb) {
+    // Check conversion of:
+    //   signed results to unsigned result to match first arg.
+    //   unsigned results to signed result to match first arg.
+    // This is the first extended instruction we've supported which goes both
+    // ways.
+    const auto assembly = Preamble() + R"(
+     %1 = OpExtInst %uint %glsl FindILsb %i1
+     %2 = OpExtInst %v2uint %glsl FindILsb %v2i1
+     %3 = OpExtInst %int %glsl FindILsb %u1
+     %4 = OpExtInst %v2int %glsl FindILsb %v2u1
+     OpReturn
+     OpFunctionEnd
+  )";
+    auto p = parser(test::Assemble(assembly));
+    ASSERT_TRUE(p->BuildAndParseInternalModuleExceptFunctions());
+    auto fe = p->function_emitter(100);
+    EXPECT_TRUE(fe.EmitBody()) << p->error();
+    auto ast_body = fe.ast_body();
+    const auto body = test::ToString(p->program(), ast_body);
+    EXPECT_THAT(body, HasSubstr(R"(
+let x_1 : u32 = bitcast<u32>(firstTrailingBit(i1));
+let x_2 : vec2<u32> = bitcast<vec2<u32>>(firstTrailingBit(v2i1));
+let x_3 : i32 = bitcast<i32>(firstTrailingBit(u1));
+let x_4 : vec2<i32> = bitcast<vec2<i32>>(firstTrailingBit(v2u1));)"))
+        << body;
+}
+
 struct DataPackingCase {
     std::string opcode;
     std::string wgsl_func;
diff --git a/src/tint/reader/spirv/parser_impl.cc b/src/tint/reader/spirv/parser_impl.cc
index b79c6634f1..38a3a05595 100644
--- a/src/tint/reader/spirv/parser_impl.cc
+++ b/src/tint/reader/spirv/parser_impl.cc
@@ -221,6 +221,7 @@ bool AssumesResultSignednessMatchesFirstOperand(GLSLstd450 extended_opcode) {
         case GLSLstd450UMin:
         case GLSLstd450UMax:
         case GLSLstd450UClamp:
+        case GLSLstd450FindILsb:
             // TODO(dneto): FindSMsb?
             // TODO(dneto): FindUMsb?
             return true;