diff --git a/dlls/mp3dmod/mp3dmod.c b/dlls/mp3dmod/mp3dmod.c
index c89f32e9ed6..5e232f0443f 100644
--- a/dlls/mp3dmod/mp3dmod.c
+++ b/dlls/mp3dmod/mp3dmod.c
@@ -52,7 +52,7 @@ struct mp3_decoder
     mpg123_handle *mh;
 
     DMO_MEDIA_TYPE intype, outtype;
-    BOOL intype_set;
+    BOOL intype_set, outtype_set;
 
     IMediaBuffer *buffer;
     REFERENCE_TIME timestamp;
@@ -262,6 +262,7 @@ static HRESULT WINAPI MediaObject_SetOutputType(IMediaObject *iface, DWORD index
     if (flags & DMO_SET_TYPEF_CLEAR)
     {
         MoFreeMediaType(&This->outtype);
+        This->outtype_set = FALSE;
         return S_OK;
     }
 
@@ -287,6 +288,7 @@ static HRESULT WINAPI MediaObject_SetOutputType(IMediaObject *iface, DWORD index
             return DMO_E_TYPE_NOT_ACCEPTED;
         }
         MoCopyMediaType(&This->outtype, type);
+        This->outtype_set = TRUE;
     }
 
     return S_OK;
@@ -306,11 +308,19 @@ static HRESULT WINAPI MediaObject_GetOutputCurrentType(IMediaObject *iface, DWOR
     return E_NOTIMPL;
 }
 
-static HRESULT WINAPI MediaObject_GetInputSizeInfo(IMediaObject *iface, DWORD index, DWORD *size, DWORD *max_lookahead, DWORD *alignment)
+static HRESULT WINAPI MediaObject_GetInputSizeInfo(IMediaObject *iface,
+        DWORD index, DWORD *size, DWORD *lookahead, DWORD *alignment)
 {
-    FIXME("(%p)->(%d, %p, %p, %p) stub!\n", iface, index, size, max_lookahead, alignment);
+    struct mp3_decoder *dmo = impl_from_IMediaObject(iface);
 
-    return E_NOTIMPL;
+    TRACE("iface %p, index %u, size %p, lookahead %p, alignment %p.\n", iface, index, size, lookahead, alignment);
+
+    if (!dmo->intype_set || !dmo->outtype_set)
+        return DMO_E_TYPE_NOT_SET;
+
+    *size = 0;
+    *alignment = 1;
+    return S_OK;
 }
 
 static HRESULT WINAPI MediaObject_GetOutputSizeInfo(IMediaObject *iface, DWORD index, DWORD *size, DWORD *alignment)
diff --git a/dlls/mp3dmod/tests/mp3dmod.c b/dlls/mp3dmod/tests/mp3dmod.c
index 1e410861eed..78471c42bcb 100644
--- a/dlls/mp3dmod/tests/mp3dmod.c
+++ b/dlls/mp3dmod/tests/mp3dmod.c
@@ -288,7 +288,36 @@ static void test_aggregation(void)
 
 static void test_stream_info(void)
 {
-    DWORD input_count, output_count, flags;
+    static const MPEGLAYER3WAVEFORMAT input_format =
+    {
+        .wfx.nChannels = 2,
+        .wfx.nSamplesPerSec = 48000,
+    };
+    DMO_MEDIA_TYPE input_mt =
+    {
+        .majortype = MEDIATYPE_Audio,
+        .subtype = WMMEDIASUBTYPE_MP3,
+        .formattype = FORMAT_WaveFormatEx,
+        .cbFormat = sizeof(input_format),
+        .pbFormat = (BYTE *)&input_format,
+    };
+
+    static const WAVEFORMATEX output_format =
+    {
+        .nChannels = 1,
+        .nSamplesPerSec = 48000,
+        .nAvgBytesPerSec = 2 * 48000,
+        .nBlockAlign = 2,
+        .wBitsPerSample = 16,
+    };
+    DMO_MEDIA_TYPE output_mt =
+    {
+        .formattype = FORMAT_WaveFormatEx,
+        .cbFormat = sizeof(output_format),
+        .pbFormat = (BYTE *)&output_format,
+    };
+
+    DWORD input_count, output_count, flags, size, lookahead, alignment;
     IMediaObject *dmo;
     HRESULT hr;
 
@@ -311,6 +340,25 @@ static void test_stream_info(void)
     ok(hr == S_OK, "Got hr %#x.\n", hr);
     ok(!flags, "Got flags %#x.\n", flags);
 
+    hr = IMediaObject_GetInputSizeInfo(dmo, 0, &size, &lookahead, &alignment);
+    ok(hr == DMO_E_TYPE_NOT_SET, "Got hr %#x.\n", hr);
+
+    hr = IMediaObject_SetInputType(dmo, 0, &input_mt, 0);
+    ok(hr == S_OK, "Got hr %#x.\n", hr);
+
+    hr = IMediaObject_GetInputSizeInfo(dmo, 0, &size, &lookahead, &alignment);
+    ok(hr == DMO_E_TYPE_NOT_SET, "Got hr %#x.\n", hr);
+
+    hr = IMediaObject_SetOutputType(dmo, 0, &output_mt, 0);
+    ok(hr == S_OK, "Got hr %#x.\n", hr);
+
+    size = lookahead = alignment = 0xdeadbeef;
+    hr = IMediaObject_GetInputSizeInfo(dmo, 0, &size, &lookahead, &alignment);
+    ok(hr == S_OK, "Got hr %#x.\n", hr);
+    ok(!size, "Got size %u.\n", size);
+    ok(lookahead == 0xdeadbeef, "Got lookahead %u.\n", lookahead);
+    ok(alignment == 1, "Got alignment %u.\n", alignment);
+
     IMediaObject_Release(dmo);
 }