diff --git a/Source/Core/Core/PowerPC/Interpreter/Interpreter_FPUtils.h b/Source/Core/Core/PowerPC/Interpreter/Interpreter_FPUtils.h
index 6c112eac66..c5d24f7a03 100644
--- a/Source/Core/Core/PowerPC/Interpreter/Interpreter_FPUtils.h
+++ b/Source/Core/Core/PowerPC/Interpreter/Interpreter_FPUtils.h
@@ -6,7 +6,6 @@
 
 #include "Common/CPUDetect.h"
 #include "Common/MathUtil.h"
-#include "Core/PowerPC/LUT_frsqrtex.h"
 #include "Core/PowerPC/Interpreter/Interpreter.h"
 
 using namespace MathUtil;
@@ -333,31 +332,68 @@ inline double ApproximateReciprocal(double val)
 
 inline double ApproximateReciprocalSquareRoot(double val)
 {
-	if (val < 0)
-		return PPC_NAN;
-	if (val == 0.0)
-		return INFINITY;
+	static const int expected_base[] = {
+		0x3ffa000, 0x3c29000, 0x38aa000, 0x3572000,
+		0x3279000, 0x2fb7000, 0x2d26000, 0x2ac0000,
+		0x2881000, 0x2665000, 0x2468000, 0x2287000,
+		0x20c1000, 0x1f12000, 0x1d79000, 0x1bf4000,
+		0x1a7e800, 0x17cb800, 0x1552800, 0x130c000,
+		0x10f2000, 0x0eff000, 0x0d2e000, 0x0b7c000,
+		0x09e5000, 0x0867000, 0x06ff000, 0x05ab800,
+		0x046a000, 0x0339800, 0x0218800, 0x0105800,
+	};
+	static const int expected_dec[] = {
+		0x7a4, 0x700, 0x670, 0x5f2,
+		0x584, 0x524, 0x4cc, 0x47e,
+		0x43a, 0x3fa, 0x3c2, 0x38e,
+		0x35e, 0x332, 0x30a, 0x2e6,
+		0x568, 0x4f3, 0x48d, 0x435,
+		0x3e7, 0x3a2, 0x365, 0x32e,
+		0x2fc, 0x2d0, 0x2a8, 0x283,
+		0x261, 0x243, 0x226, 0x20b,
+	};
 
-	union
-	{
+	union {
 		double valf;
-		u64 vali;
+		long long vali;
 	};
 	valf = val;
+	long long mantissa = vali & ((1LL << 52) - 1);
+	long long sign = vali & (1ULL << 63);
+	long long exponent = vali & (0x7FFLL << 52);
 
-	u32 fsa = vali >> 32;
-	u32 idx = (fsa >> 5) % (sizeof(frsqrtex_lut) / sizeof(frsqrtex_lut[0]));
+	// Special case 0
+	if (mantissa == 0 && exponent == 0)
+		return sign ? -INFINITY : INFINITY;
+	// Special case NaN-ish numbers
+	if (exponent == (0x7FFLL << 52))
+	{
+		if (mantissa == 0)
+			return sign ? NAN : 0.0;
+		return 0.0 + valf;
+	}
+	// Negative numbers return NaN
+	if (sign)
+		return NAN;
 
-	s32 e = fsa >> (32 - 12);
-	e &= 2047;
-	e -= 1023;
-	s32 oe = -((e + 1) / 2);
-	oe -= ((e + 1) & 1);
+	if (!exponent)
+	{
+		// "Normalize" denormal values
+		do
+		{
+			exponent -= 1LL << 52;
+			mantissa <<= 1;
+		} while (!(mantissa & (1LL << 52)));
+		mantissa &= (1LL << 52) - 1;
+		exponent += 1LL << 52;
+	}
 
-	u32 outb = frsqrtex_lut[idx] << 20;
-	u32 outa = ((oe + 1023) & 2047) << 20;
-	outa |= frsqrtex_lut[idx] >> 12;
+	bool odd_exponent = !(exponent & (1LL << 52));
+	exponent = ((0x3FFLL << 52) - ((exponent - (0x3FELL << 52)) / 2)) & (0x7FFLL << 52);
 
-	vali = ((u64)outa << 32) + (u64)outb;
+	int i = (int)(mantissa >> 37);
+	vali = sign | exponent;
+	int index = i / 2048 + (odd_exponent ? 16 : 0);
+	vali |= (long long)(expected_base[index] - expected_dec[index] * (i % 2048)) << 26;
 	return valf;
 }