diff --git a/src/main/java/org/apache/commons/lang3/Conversion.java b/src/main/java/org/apache/commons/lang3/Conversion.java
index b91e52e765f..cf43e36c371 100644
--- a/src/main/java/org/apache/commons/lang3/Conversion.java
+++ b/src/main/java/org/apache/commons/lang3/Conversion.java
@@ -160,7 +160,7 @@ public static byte binaryToByte(final boolean[] src, final int srcPos, final byt
         if (src.length == 0 && srcPos == 0 || 0 == nBools) {
             return dstInit;
         }
-        if (nBools - 1 + dstPos >= Byte.SIZE) {
+        if ((long) nBools - 1 + dstPos >= Byte.SIZE) {
             throw new IllegalArgumentException("nBools - 1 + dstPos >= 8");
         }
         byte out = dstInit;
@@ -307,7 +307,7 @@ public static int binaryToInt(final boolean[] src, final int srcPos, final int d
         if (src.length == 0 && srcPos == 0 || 0 == nBools) {
             return dstInit;
         }
-        if (nBools - 1 + dstPos >= Integer.SIZE) {
+        if ((long) nBools - 1 + dstPos >= Integer.SIZE) {
             throw new IllegalArgumentException("nBools - 1 + dstPos >= 32");
         }
         int out = dstInit;
@@ -337,7 +337,7 @@ public static long binaryToLong(final boolean[] src, final int srcPos, final lon
         if (src.length == 0 && srcPos == 0 || 0 == nBools) {
             return dstInit;
         }
-        if (nBools - 1 + dstPos >= Long.SIZE) {
+        if ((long) nBools - 1 + dstPos >= Long.SIZE) {
             throw new IllegalArgumentException("nBools - 1 + dstPos >= 64");
         }
         long out = dstInit;
@@ -367,7 +367,7 @@ public static short binaryToShort(final boolean[] src, final int srcPos, final s
         if (src.length == 0 && srcPos == 0 || 0 == nBools) {
             return dstInit;
         }
-        if (nBools - 1 + dstPos >= Short.SIZE) {
+        if ((long) nBools - 1 + dstPos >= Short.SIZE) {
             throw new IllegalArgumentException("nBools - 1 + dstPos >= 16");
         }
         short out = dstInit;
@@ -397,7 +397,7 @@ public static int byteArrayToInt(final byte[] src, final int srcPos, final int d
         if (src.length == 0 && srcPos == 0 || 0 == nBytes) {
             return dstInit;
         }
-        if ((nBytes - 1) * Byte.SIZE + dstPos >= Integer.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + dstPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + dstPos >= 32");
         }
         int out = dstInit;
@@ -427,7 +427,7 @@ public static long byteArrayToLong(final byte[] src, final int srcPos, final lon
         if (src.length == 0 && srcPos == 0 || 0 == nBytes) {
             return dstInit;
         }
-        if ((nBytes - 1) * Byte.SIZE + dstPos >= Long.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + dstPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + dstPos >= 64");
         }
         long out = dstInit;
@@ -457,7 +457,7 @@ public static short byteArrayToShort(final byte[] src, final int srcPos, final s
         if (src.length == 0 && srcPos == 0 || 0 == nBytes) {
             return dstInit;
         }
-        if ((nBytes - 1) * Byte.SIZE + dstPos >= Short.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + dstPos >= Short.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + dstPos >= 16");
         }
         short out = dstInit;
@@ -503,7 +503,7 @@ public static boolean[] byteToBinary(final byte src, final int srcPos, final boo
         if (0 == nBools) {
             return dst;
         }
-        if (nBools - 1 + srcPos >= Byte.SIZE) {
+        if ((long) nBools - 1 + srcPos >= Byte.SIZE) {
             throw new IllegalArgumentException("nBools -  1 + srcPos >= 8");
         }
         for (int i = 0; i < nBools; i++) {
@@ -529,7 +529,7 @@ public static String byteToHex(final byte src, final int srcPos, final String ds
         if (0 == nHexs) {
             return dstInit;
         }
-        if ((nHexs - 1) * 4 + srcPos >= Byte.SIZE) {
+        if (((long) nHexs - 1) * 4 + srcPos >= Byte.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + srcPos >= 8");
         }
         final StringBuilder sb = new StringBuilder(dstInit);
@@ -748,7 +748,7 @@ public static byte hexToByte(final String src, final int srcPos, final byte dstI
         if (0 == nHex) {
             return dstInit;
         }
-        if ((nHex - 1) * 4 + dstPos >= Byte.SIZE) {
+        if (((long) nHex - 1) * 4 + dstPos >= Byte.SIZE) {
             throw new IllegalArgumentException("(nHex - 1) * 4 + dstPos >= 8");
         }
         byte out = dstInit;
@@ -776,7 +776,7 @@ public static int hexToInt(final String src, final int srcPos, final int dstInit
         if (0 == nHex) {
             return dstInit;
         }
-        if ((nHex - 1) * 4 + dstPos >= Integer.SIZE) {
+        if (((long) nHex - 1) * 4 + dstPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + dstPos >= 32");
         }
         int out = dstInit;
@@ -804,7 +804,7 @@ public static long hexToLong(final String src, final int srcPos, final long dstI
         if (0 == nHex) {
             return dstInit;
         }
-        if ((nHex - 1) * 4 + dstPos >= Long.SIZE) {
+        if (((long) nHex - 1) * 4 + dstPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + dstPos >= 64");
         }
         long out = dstInit;
@@ -832,7 +832,7 @@ public static short hexToShort(final String src, final int srcPos, final short d
         if (0 == nHex) {
             return dstInit;
         }
-        if ((nHex - 1) * 4 + dstPos >= Short.SIZE) {
+        if (((long) nHex - 1) * 4 + dstPos >= Short.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + dstPos >= 16");
         }
         short out = dstInit;
@@ -862,7 +862,7 @@ public static long intArrayToLong(final int[] src, final int srcPos, final long
         if (src.length == 0 && srcPos == 0 || 0 == nInts) {
             return dstInit;
         }
-        if ((nInts - 1) * Integer.SIZE + dstPos >= Long.SIZE) {
+        if (((long) nInts - 1) * Integer.SIZE + dstPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nInts - 1) * 32 + dstPos >= 64");
         }
         long out = dstInit;
@@ -892,7 +892,7 @@ public static boolean[] intToBinary(final int src, final int srcPos, final boole
         if (0 == nBools) {
             return dst;
         }
-        if (nBools - 1 + srcPos >= Integer.SIZE) {
+        if ((long) nBools - 1 + srcPos >= Integer.SIZE) {
             throw new IllegalArgumentException("nBools -  1 + srcPos >= 32");
         }
         for (int i = 0; i < nBools; i++) {
@@ -919,7 +919,7 @@ public static byte[] intToByteArray(final int src, final int srcPos, final byte[
         if (0 == nBytes) {
             return dst;
         }
-        if ((nBytes - 1) * Byte.SIZE + srcPos >= Integer.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + srcPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + srcPos >= 32");
         }
         for (int i = 0; i < nBytes; i++) {
@@ -945,7 +945,7 @@ public static String intToHex(final int src, final int srcPos, final String dstI
         if (0 == nHexs) {
             return dstInit;
         }
-        if ((nHexs - 1) * 4 + srcPos >= Integer.SIZE) {
+        if (((long) nHexs - 1) * 4 + srcPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + srcPos >= 32");
         }
         final StringBuilder sb = new StringBuilder(dstInit);
@@ -1061,7 +1061,7 @@ public static short[] intToShortArray(final int src, final int srcPos, final sho
         if (0 == nShorts) {
             return dst;
         }
-        if ((nShorts - 1) * Short.SIZE + srcPos >= Integer.SIZE) {
+        if (((long) nShorts - 1) * Short.SIZE + srcPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nShorts - 1) * 16 + srcPos >= 32");
         }
         for (int i = 0; i < nShorts; i++) {
@@ -1088,7 +1088,7 @@ public static boolean[] longToBinary(final long src, final int srcPos, final boo
         if (0 == nBools) {
             return dst;
         }
-        if (nBools - 1 + srcPos >= Long.SIZE) {
+        if ((long) nBools - 1 + srcPos >= Long.SIZE) {
             throw new IllegalArgumentException("nBools -  1 + srcPos >= 64");
         }
         for (int i = 0; i < nBools; i++) {
@@ -1115,7 +1115,7 @@ public static byte[] longToByteArray(final long src, final int srcPos, final byt
         if (0 == nBytes) {
             return dst;
         }
-        if ((nBytes - 1) * Byte.SIZE + srcPos >= Long.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + srcPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + srcPos >= 64");
         }
         for (int i = 0; i < nBytes; i++) {
@@ -1141,7 +1141,7 @@ public static String longToHex(final long src, final int srcPos, final String ds
         if (0 == nHexs) {
             return dstInit;
         }
-        if ((nHexs - 1) * 4 + srcPos >= Long.SIZE) {
+        if (((long) nHexs - 1) * 4 + srcPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + srcPos >= 64");
         }
         final StringBuilder sb = new StringBuilder(dstInit);
@@ -1176,7 +1176,7 @@ public static int[] longToIntArray(final long src, final int srcPos, final int[]
         if (0 == nInts) {
             return dst;
         }
-        if ((nInts - 1) * Integer.SIZE + srcPos >= Long.SIZE) {
+        if (((long) nInts - 1) * Integer.SIZE + srcPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nInts - 1) * 32 + srcPos >= 64");
         }
         for (int i = 0; i < nInts; i++) {
@@ -1203,7 +1203,7 @@ public static short[] longToShortArray(final long src, final int srcPos, final s
         if (0 == nShorts) {
             return dst;
         }
-        if ((nShorts - 1) * Short.SIZE + srcPos >= Long.SIZE) {
+        if (((long) nShorts - 1) * Short.SIZE + srcPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nShorts - 1) * 16 + srcPos >= 64");
         }
         for (int i = 0; i < nShorts; i++) {
@@ -1230,7 +1230,7 @@ public static int shortArrayToInt(final short[] src, final int srcPos, final int
         if (src.length == 0 && srcPos == 0 || 0 == nShorts) {
             return dstInit;
         }
-        if ((nShorts - 1) * Short.SIZE + dstPos >= Integer.SIZE) {
+        if (((long) nShorts - 1) * Short.SIZE + dstPos >= Integer.SIZE) {
             throw new IllegalArgumentException("(nShorts - 1) * 16 + dstPos >= 32");
         }
         int out = dstInit;
@@ -1260,7 +1260,7 @@ public static long shortArrayToLong(final short[] src, final int srcPos, final l
         if (src.length == 0 && srcPos == 0 || 0 == nShorts) {
             return dstInit;
         }
-        if ((nShorts - 1) * Short.SIZE + dstPos >= Long.SIZE) {
+        if (((long) nShorts - 1) * Short.SIZE + dstPos >= Long.SIZE) {
             throw new IllegalArgumentException("(nShorts - 1) * 16 + dstPos >= 64");
         }
         long out = dstInit;
@@ -1290,7 +1290,7 @@ public static boolean[] shortToBinary(final short src, final int srcPos, final b
         if (0 == nBools) {
             return dst;
         }
-        if (nBools - 1 + srcPos >= Short.SIZE) {
+        if ((long) nBools - 1 + srcPos >= Short.SIZE) {
             throw new IllegalArgumentException("nBools -  1 + srcPos >= 16");
         }
         assert nBools - 1 < Short.SIZE - srcPos;
@@ -1318,7 +1318,7 @@ public static byte[] shortToByteArray(final short src, final int srcPos, final b
         if (0 == nBytes) {
             return dst;
         }
-        if ((nBytes - 1) * Byte.SIZE + srcPos >= Short.SIZE) {
+        if (((long) nBytes - 1) * Byte.SIZE + srcPos >= Short.SIZE) {
             throw new IllegalArgumentException("(nBytes - 1) * 8 + srcPos >= 16");
         }
         for (int i = 0; i < nBytes; i++) {
@@ -1344,7 +1344,7 @@ public static String shortToHex(final short src, final int srcPos, final String
         if (0 == nHexs) {
             return dstInit;
         }
-        if ((nHexs - 1) * 4 + srcPos >= Short.SIZE) {
+        if (((long) nHexs - 1) * 4 + srcPos >= Short.SIZE) {
             throw new IllegalArgumentException("(nHexs - 1) * 4 + srcPos >= 16");
         }
         final StringBuilder sb = new StringBuilder(dstInit);
diff --git a/src/test/java/org/apache/commons/lang3/ConversionTest.java b/src/test/java/org/apache/commons/lang3/ConversionTest.java
index b0b31630162..9b475a9b339 100644
--- a/src/test/java/org/apache/commons/lang3/ConversionTest.java
+++ b/src/test/java/org/apache/commons/lang3/ConversionTest.java
@@ -1729,4 +1729,49 @@ void testUuidToByteArray() {
         assertIllegalArgumentException(() -> Conversion.uuidToByteArray(new UUID(
                 0xFFEEDDCCBBAA9988L, 0x7766554433221100L), new byte[16], 2, 17));
     }
+
+    /**
+     * Each converter documents an {@link IllegalArgumentException} when the requested count and position exceed the destination width, but the guard was
+     * evaluated in {@code int} arithmetic and silently overflowed for a large count or position, so the documented exception never fired.
+     */
+    @Test
+    void testOverflowingCountOrPositionThrowsIllegalArgumentException() {
+        final int big = Integer.MAX_VALUE;
+        // nBools - 1 + dstPos
+        assertIllegalArgumentException(() -> Conversion.binaryToByte(new boolean[]{true}, 0, (byte) 0, big, 2));
+        assertIllegalArgumentException(() -> Conversion.binaryToInt(new boolean[]{true}, 0, 0, big, 2));
+        assertIllegalArgumentException(() -> Conversion.binaryToLong(new boolean[]{true}, 0, 0L, big, 2));
+        assertIllegalArgumentException(() -> Conversion.binaryToShort(new boolean[]{true}, 0, (short) 0, big, 2));
+        // nBools - 1 + srcPos
+        assertIllegalArgumentException(() -> Conversion.byteToBinary((byte) 1, big, new boolean[8], 0, 2));
+        assertIllegalArgumentException(() -> Conversion.intToBinary(0, big, new boolean[32], 0, 2));
+        assertIllegalArgumentException(() -> Conversion.longToBinary(0L, big, new boolean[64], 0, 2));
+        assertIllegalArgumentException(() -> Conversion.shortToBinary((short) 0, big, new boolean[16], 0, 2));
+        // (nBytes - 1) * 8 + dstPos
+        assertIllegalArgumentException(() -> Conversion.byteArrayToInt(new byte[]{1}, 0, 0, 0, big));
+        assertIllegalArgumentException(() -> Conversion.byteArrayToLong(new byte[]{1}, 0, 0L, 0, big));
+        assertIllegalArgumentException(() -> Conversion.byteArrayToShort(new byte[]{1}, 0, (short) 0, 0, big));
+        // (nBytes - 1) * 8 + srcPos
+        assertIllegalArgumentException(() -> Conversion.intToByteArray(0, 0, new byte[4], 0, big));
+        assertIllegalArgumentException(() -> Conversion.longToByteArray(0L, 0, new byte[8], 0, big));
+        assertIllegalArgumentException(() -> Conversion.shortToByteArray((short) 0, 0, new byte[2], 0, big));
+        // (nHex - 1) * 4 + dstPos
+        assertIllegalArgumentException(() -> Conversion.hexToByte("f", 0, (byte) 0, 0, big));
+        assertIllegalArgumentException(() -> Conversion.hexToInt("f", 0, 0, 0, big));
+        assertIllegalArgumentException(() -> Conversion.hexToLong("f", 0, 0L, 0, big));
+        assertIllegalArgumentException(() -> Conversion.hexToShort("f", 0, (short) 0, 0, big));
+        // (nHexs - 1) * 4 + srcPos
+        assertIllegalArgumentException(() -> Conversion.byteToHex((byte) 0, 0, "", 0, big));
+        assertIllegalArgumentException(() -> Conversion.intToHex(0, 0, "", 0, big));
+        assertIllegalArgumentException(() -> Conversion.longToHex(0L, 0, "", 0, big));
+        assertIllegalArgumentException(() -> Conversion.shortToHex((short) 0, 0, "", 0, big));
+        // (nInts - 1) * 32 + pos
+        assertIllegalArgumentException(() -> Conversion.intArrayToLong(new int[]{0}, 0, 0L, 0, big));
+        assertIllegalArgumentException(() -> Conversion.longToIntArray(0L, 0, new int[2], 0, big));
+        // (nShorts - 1) * 16 + pos
+        assertIllegalArgumentException(() -> Conversion.shortArrayToInt(new short[]{0}, 0, 0, 0, big));
+        assertIllegalArgumentException(() -> Conversion.shortArrayToLong(new short[]{0}, 0, 0L, 0, big));
+        assertIllegalArgumentException(() -> Conversion.intToShortArray(0, 0, new short[2], 0, big));
+        assertIllegalArgumentException(() -> Conversion.longToShortArray(0L, 0, new short[4], 0, big));
+    }
 }