diff --git a/src/api/API.jl b/src/api/API.jl
index f4e0332..502ea16 100644
--- a/src/api/API.jl
+++ b/src/api/API.jl
@@ -229,14 +229,14 @@ _msgsizeof_parts(parts::Tuple) = msgsizeof(first(parts)) + _msgsizeof_parts(Base
 
 writepart(io, x) = write(io, x)
 function writepart(io, x::String)
-    occursin('\0', x) && throw(Postgres.PostgresInterfaceError("PostgreSQL protocol strings cannot contain a NUL byte"))
+    occursin('\0', x) && throw(PostgresInterfaceError("PostgreSQL protocol strings cannot contain a NUL byte"))
     write(io, x)
     write(io, UInt8(0))
 end
 writepart(io, x::Integer) = write(io, hton(x))
 function writepart(io, x::Tuple{String, String})
     (occursin('\0', x[1]) || occursin('\0', x[2])) &&
-        throw(Postgres.PostgresInterfaceError("PostgreSQL startup parameters cannot contain a NUL byte"))
+        throw(PostgresInterfaceError("PostgreSQL startup parameters cannot contain a NUL byte"))
     write(io, x[1])
     write(io, UInt8(0))
     write(io, x[2])
diff --git a/test/runtests.jl b/test/runtests.jl
index 71a4f5a..c76008f 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -983,6 +983,14 @@ include("notification_deadlines.jl")
         end
     end
 
+    @testset "Protocol Strings Reject NUL" begin
+        # the message is still buffered when the check throws, so nothing is sent
+        io = IOBuffer()
+        @test_throws Postgres.PostgresInterfaceError Postgres.API.writemessage(io, false, 'Q', "SELECT 1\0")
+        @test_throws Postgres.PostgresInterfaceError Postgres.API.writepart(io, ("user", "a\0b"))
+        @test position(io) == 0
+    end
+
     @testset "Seeded Protocol And DSN Fuzz" begin
         rng = MersenneTwister(0xf022)
         registry = Dict(Postgres.API.DEFAULT_TYPE_REGISTRY)
@@ -1142,6 +1150,10 @@ include("notification_deadlines.jl")
                     @test isopen(connp.socket)
                     @test Tables.rowtable(DBInterface.execute(connp, "SELECT 1 AS a"))[1].a == 1
 
+                    # SQL with a NUL byte is rejected before anything is sent
+                    @test_throws Postgres.PostgresInterfaceError DBInterface.execute(connp, "SELECT 1\0")
+                    @test Tables.rowtable(DBInterface.execute(connp, "SELECT 1 AS a"))[1].a == 1
+
                     # a consumer exception mid-result drains the remaining rows so
                     # the connection stays usable
                     stmt = DBInterface.prepare(connp, "SELECT i AS x, repeat('y', 10) AS s FROM generate_series(1, 200) i")