diff --git a/GPU/Common/GPUStateUtils.cpp b/GPU/Common/GPUStateUtils.cpp
index b2f46e0d09..b2d17e7f17 100644
--- a/GPU/Common/GPUStateUtils.cpp
+++ b/GPU/Common/GPUStateUtils.cpp
@@ -1119,3 +1119,125 @@ void ConvertBlendState(GenericBlendState &blendState, bool allowShaderBlend) {
 		blendState.setEquation(eqLookupNoMinMax[blendFuncEq], alphaEq);
 	}
 }
+
+void ConvertStencilFuncState(GenericStencilFuncState &state) {
+	state.enabled = gstate.isStencilTestEnabled() && !g_Config.bDisableStencilTest;
+	if (!state.enabled)
+		return;
+
+	// The PSP's mask is reversed (bits not to write.)
+	state.writeMask = (~(gstate.pmska >> 0)) & 0xFF;
+
+	state.sFail = gstate.getStencilOpSFail();
+	state.zFail = gstate.getStencilOpZFail();
+	state.zPass = gstate.getStencilOpZPass();
+
+	state.testFunc = gstate.getStencilTestFunction();
+	state.testRef = gstate.getStencilTestRef();
+	state.testMask = gstate.getStencilTestMask();
+
+	bool usesRef = state.sFail == GE_STENCILOP_REPLACE || state.zFail == GE_STENCILOP_REPLACE || state.zPass == GE_STENCILOP_REPLACE;
+	switch (gstate.FrameBufFormat()) {
+	case GE_FORMAT_565:
+		state.writeMask = 0;
+		break;
+
+	case GE_FORMAT_5551:
+		state.writeMask = state.writeMask >= 0x80 ? 0xff : 0x00;
+
+		// Decrement always zeros, so let's rewrite those to be safe (even if it's not 1.)
+		if (state.sFail == GE_STENCILOP_DECR)
+			state.sFail = GE_STENCILOP_ZERO;
+		if (state.zFail == GE_STENCILOP_DECR)
+			state.zFail = GE_STENCILOP_ZERO;
+		if (state.zPass == GE_STENCILOP_DECR)
+			state.zPass = GE_STENCILOP_ZERO;
+
+		if (!usesRef) {
+			// For 5551, we treat any non-zero value in the buffer as 255.  Only zero is treated as zero.
+			// See: https://github.com/hrydgard/ppsspp/pull/4150#issuecomment-26211193
+			switch (state.testFunc) {
+			case GE_COMP_NEVER:
+			case GE_COMP_ALWAYS:
+				// Fine as is.
+				break;
+			case GE_COMP_EQUAL:
+				if (state.testRef == 255) {
+					if (!usesRef) {
+						state.testFunc = GE_COMP_NOTEQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				} else if (state.testRef != 0) {
+					// This should never pass, regardless of buffer value.  Only 0 and 255 are directly equal.
+					state.testFunc = GE_COMP_NEVER;
+				}
+				break;
+			case GE_COMP_NOTEQUAL:
+				if (state.testRef == 255) {
+					if (!usesRef) {
+						state.testFunc = GE_COMP_EQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				} else if (state.testRef != 0) {
+					state.testFunc = GE_COMP_ALWAYS;
+				}
+				break;
+			case GE_COMP_LESS:
+				if (state.testRef == 255) {
+					state.testFunc = GE_COMP_NEVER;
+				} else {
+					if (!usesRef || state.testRef == 0) {
+						// Any non-zero value in the buffer should be treated as 255.
+						state.testFunc = GE_COMP_NOTEQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				}
+				break;
+			case GE_COMP_LEQUAL:
+				if (state.testRef == 0) {
+					state.testFunc = GE_COMP_ALWAYS;
+				} else {
+					if (!usesRef) {
+						// Everything but 0 in the buffer is "255", so only 0 doesn't match.
+						state.testFunc = GE_COMP_NOTEQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				}
+				break;
+			case GE_COMP_GREATER:
+				if (state.testRef > 0) {
+					if (!usesRef) {
+						// If we have a 1 in the buffer, it's the same as 255, which > can never match.
+						state.testFunc = GE_COMP_EQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				} else {
+					state.testFunc = GE_COMP_NEVER;
+				}
+				break;
+			case GE_COMP_GEQUAL:
+				if (state.testRef == 255) {
+					state.testFunc = GE_COMP_ALWAYS;
+				} else {
+					if (!usesRef || state.testRef == 0) {
+						// If the buffer is non-zero, we treat as 255.  So only 0 can match.
+						state.testFunc = GE_COMP_EQUAL;
+						state.testRef = 0;
+						state.testMask = 255;
+					}
+				}
+				break;
+			}
+		}
+		break;
+
+	default:
+		// Hard to do anything useful for 4444, and 8888 is fine.
+		break;
+	}
+}
diff --git a/GPU/Common/GPUStateUtils.h b/GPU/Common/GPUStateUtils.h
index f7a2c53685..b3c398db11 100644
--- a/GPU/Common/GPUStateUtils.h
+++ b/GPU/Common/GPUStateUtils.h
@@ -137,3 +137,16 @@ struct GenericBlendState {
 
 void ConvertBlendState(GenericBlendState &blendState, bool allowShaderBlend);
 void ApplyStencilReplaceAndLogicOp(ReplaceAlphaType replaceAlphaWithStencil, GenericBlendState &blendState);
+
+struct GenericStencilFuncState {
+	bool enabled;
+	GEComparison testFunc;
+	u8 testRef;
+	u8 testMask;
+	u8 writeMask;
+	GEStencilOp sFail;
+	GEStencilOp zFail;
+	GEStencilOp zPass;
+};
+
+void ConvertStencilFuncState(GenericStencilFuncState &stencilFuncState);
diff --git a/GPU/Directx9/StateMappingDX9.cpp b/GPU/Directx9/StateMappingDX9.cpp
index 94e9df4841..feb008488d 100644
--- a/GPU/Directx9/StateMappingDX9.cpp
+++ b/GPU/Directx9/StateMappingDX9.cpp
@@ -243,8 +243,8 @@ void TransformDrawEngineDX9::ApplyDrawState(int prim) {
 		bool bmask = ((gstate.pmskc >> 16) & 0xFF) < 128;
 		bool amask = (gstate.pmska & 0xFF) < 128;
 
-		u8 abits = (gstate.pmska >> 0) & 0xFF;
 #ifndef MOBILE_DEVICE
+		u8 abits = (gstate.pmska >> 0) & 0xFF;
 		u8 rbits = (gstate.pmskc >> 0) & 0xFF;
 		u8 gbits = (gstate.pmskc >> 8) & 0xFF;
 		u8 bbits = (gstate.pmskc >> 16) & 0xFF;
@@ -268,21 +268,16 @@ void TransformDrawEngineDX9::ApplyDrawState(int prim) {
 		}
 
 		dxstate.colorMask.set(rmask, gmask, bmask, amask);
-		
+
+		GenericStencilFuncState stencilState;
+		ConvertStencilFuncState(stencilState);
+
 		// Stencil Test
-		if (gstate.isStencilTestEnabled()) {
+		if (stencilState.enabled) {
 			dxstate.stencilTest.enable();
-			dxstate.stencilFunc.set(ztests[gstate.getStencilTestFunction()],
-				gstate.getStencilTestRef(),
-				gstate.getStencilTestMask());
-			dxstate.stencilOp.set(stencilOps[gstate.getStencilOpSFail()],  // stencil fail
-				stencilOps[gstate.getStencilOpZFail()],  // depth fail
-				stencilOps[gstate.getStencilOpZPass()]); // depth pass
-			if (gstate.FrameBufFormat() == GE_FORMAT_5551) {
-				dxstate.stencilMask.set(abits <= 0x7f ? 0xff : 0x00);
-			} else {
-				dxstate.stencilMask.set(~abits);
-			}
+			dxstate.stencilFunc.set(ztests[stencilState.testFunc], stencilState.testRef, stencilState.testMask);
+			dxstate.stencilOp.set(stencilOps[stencilState.sFail], stencilOps[stencilState.zFail], stencilOps[stencilState.zPass]);
+			dxstate.stencilMask.set(stencilState.writeMask);
 		} else {
 			dxstate.stencilTest.disable();
 		}
diff --git a/GPU/GLES/StateMapping.cpp b/GPU/GLES/StateMapping.cpp
index 840803ba9c..fb433472f5 100644
--- a/GPU/GLES/StateMapping.cpp
+++ b/GPU/GLES/StateMapping.cpp
@@ -312,8 +312,8 @@ void TransformDrawEngine::ApplyDrawState(int prim) {
 		bool bmask = ((gstate.pmskc >> 16) & 0xFF) < 128;
 		bool amask = (gstate.pmska & 0xFF) < 128;
 
-		u8 abits = (gstate.pmska >> 0) & 0xFF;
 #ifndef MOBILE_DEVICE
+		u8 abits = (gstate.pmska >> 0) & 0xFF;
 		u8 rbits = (gstate.pmskc >> 0) & 0xFF;
 		u8 gbits = (gstate.pmskc >> 8) & 0xFF;
 		u8 bbits = (gstate.pmskc >> 16) & 0xFF;
@@ -338,21 +338,15 @@ void TransformDrawEngine::ApplyDrawState(int prim) {
 
 		glstate.colorMask.set(rmask, gmask, bmask, amask);
 
-		// Stencil Test
-		if (gstate.isStencilTestEnabled() && enableStencilTest) {
-			glstate.stencilTest.enable();
-			glstate.stencilFunc.set(ztests[gstate.getStencilTestFunction()],
-				gstate.getStencilTestRef(),
-				gstate.getStencilTestMask());
-			glstate.stencilOp.set(stencilOps[gstate.getStencilOpSFail()],  // stencil fail
-				stencilOps[gstate.getStencilOpZFail()],  // depth fail
-				stencilOps[gstate.getStencilOpZPass()]); // depth pass
+		GenericStencilFuncState stencilState;
+		ConvertStencilFuncState(stencilState);
 
-			if (gstate.FrameBufFormat() == GE_FORMAT_5551) {
-				glstate.stencilMask.set(abits <= 0x7f ? 0xff : 0x00);
-			} else {
-				glstate.stencilMask.set(~abits);
-			}
+		// Stencil Test
+		if (stencilState.enabled) {
+			glstate.stencilTest.enable();
+			glstate.stencilFunc.set(ztests[stencilState.testFunc], stencilState.testRef, stencilState.testMask);
+			glstate.stencilOp.set(stencilOps[stencilState.sFail], stencilOps[stencilState.zFail], stencilOps[stencilState.zPass]);
+			glstate.stencilMask.set(stencilState.writeMask);
 		} else {
 			glstate.stencilTest.disable();
 		}