diff --git a/.changeset/fix-electric-null-params.md b/.changeset/fix-electric-null-params.md
new file mode 100644
index 000000000..9effab7e3
--- /dev/null
+++ b/.changeset/fix-electric-null-params.md
@@ -0,0 +1,9 @@
+---
+'@tanstack/electric-db-collection': patch
+---
+
+Fix invalid Electric proxy queries with missing params for null/undefined values
+
+When comparison operators were used with null/undefined values, the SQL compiler would generate placeholders ($1, $2) in the WHERE clause but skip adding the params to the dictionary. This resulted in invalid queries being sent to Electric.
+
+Now all comparison operators (eq, gt, lt, gte, lte, like, ilike) throw a clear error when used with null/undefined values, since comparisons with NULL always evaluate to UNKNOWN in SQL. Users should use `isNull()` or `isUndefined()` to check for null values instead.
diff --git a/packages/electric-db-collection/src/sql-compiler.ts b/packages/electric-db-collection/src/sql-compiler.ts
index 6c1db6c4c..d7d021c89 100644
--- a/packages/electric-db-collection/src/sql-compiler.ts
+++ b/packages/electric-db-collection/src/sql-compiler.ts
@@ -124,6 +124,13 @@ function compileOrderByClause(
   return sql
 }
 
+/**
+ * Check if a BasicExpression represents a null/undefined value
+ */
+function isNullValue(exp: IR.BasicExpression<unknown>): boolean {
+  return exp.type === `val` && (exp.value === null || exp.value === undefined)
+}
+
 function compileFunction(
   exp: IR.Func<unknown>,
   params: Array<unknown> = [],
@@ -132,6 +139,26 @@ function compileFunction(
 
   const opName = getOpName(name)
 
+  // Handle comparison operators with null/undefined values
+  // These would create invalid queries with missing params (e.g., "col = $1" with empty params)
+  // In SQL, all comparisons with NULL return UNKNOWN, so these are almost always mistakes
+  if (isComparisonOp(name)) {
+    const nullArgIndex = args.findIndex((arg: IR.BasicExpression) =>
+      isNullValue(arg),
+    )
+
+    if (nullArgIndex !== -1) {
+      // All comparison operators (including eq) throw an error for null values
+      // Users should use isNull() or isUndefined() to check for null values
+      throw new Error(
+        `Cannot use null/undefined value with '${name}' operator. ` +
+          `Comparisons with null always evaluate to UNKNOWN in SQL. ` +
+          `Use isNull() or isUndefined() to check for null values, ` +
+          `or filter out null values before building the query.`,
+      )
+    }
+  }
+
   const compiledArgs = args.map((arg: IR.BasicExpression) =>
     compileBasicExpression(arg, params),
   )
@@ -176,7 +203,7 @@ function compileFunction(
     // Special case for comparison operators with boolean values
     // PostgreSQL doesn't support < > <= >= on booleans
     // Transform to equivalent equality checks or constant expressions
-    if (isComparisonOp(name)) {
+    if (isBooleanComparisonOp(name)) {
       const lhsArg = args[0]
       const rhsArg = args[1]
 
@@ -312,11 +339,21 @@ function isBinaryOp(name: string): boolean {
   return binaryOps.includes(name)
 }
 
+/**
+ * Check if operator is a comparison operator that takes two values
+ * These operators cannot accept null/undefined as values
+ * (null comparisons in SQL always evaluate to UNKNOWN)
+ */
+function isComparisonOp(name: string): boolean {
+  const comparisonOps = [`eq`, `gt`, `gte`, `lt`, `lte`, `like`, `ilike`]
+  return comparisonOps.includes(name)
+}
+
 /**
  * Checks if the operator is a comparison operator (excluding eq)
  * These operators don't work on booleans in PostgreSQL without casting
  */
-function isComparisonOp(name: string): boolean {
+function isBooleanComparisonOp(name: string): boolean {
   return [`gt`, `gte`, `lt`, `lte`].includes(name)
 }
 
diff --git a/packages/electric-db-collection/tests/sql-compiler.test.ts b/packages/electric-db-collection/tests/sql-compiler.test.ts
new file mode 100644
index 000000000..9989d47f9
--- /dev/null
+++ b/packages/electric-db-collection/tests/sql-compiler.test.ts
@@ -0,0 +1,312 @@
+import { describe, expect, it } from 'vitest'
+import { compileSQL } from '../src/sql-compiler'
+import type { IR } from '@tanstack/db'
+
+// Helper to create a value expression
+function val<T>(value: T): IR.BasicExpression<T> {
+  return { type: `val`, value } as IR.BasicExpression<T>
+}
+
+// Helper to create a reference expression
+function ref(...path: Array<string>): IR.BasicExpression {
+  return { type: `ref`, path } as IR.BasicExpression
+}
+
+// Helper to create a function expression
+
+function func(name: string, args: Array<any>): IR.BasicExpression<boolean> {
+  return { type: `func`, name, args } as IR.BasicExpression<boolean>
+}
+
+describe(`sql-compiler`, () => {
+  describe(`compileSQL`, () => {
+    describe(`basic where clauses`, () => {
+      it(`should compile eq with string value`, () => {
+        const result = compileSQL({
+          where: func(`eq`, [ref(`name`), val(`John`)]),
+        })
+        expect(result.where).toBe(`"name" = $1`)
+        expect(result.params).toEqual({ '1': `John` })
+      })
+
+      it(`should compile eq with number value`, () => {
+        const result = compileSQL({
+          where: func(`eq`, [ref(`age`), val(25)]),
+        })
+        expect(result.where).toBe(`"age" = $1`)
+        expect(result.params).toEqual({ '1': `25` })
+      })
+
+      it(`should compile gt operator`, () => {
+        const result = compileSQL({
+          where: func(`gt`, [ref(`age`), val(18)]),
+        })
+        expect(result.where).toBe(`"age" > $1`)
+        expect(result.params).toEqual({ '1': `18` })
+      })
+
+      it(`should compile lt operator`, () => {
+        const result = compileSQL({
+          where: func(`lt`, [ref(`price`), val(100)]),
+        })
+        expect(result.where).toBe(`"price" < $1`)
+        expect(result.params).toEqual({ '1': `100` })
+      })
+
+      it(`should compile gte operator`, () => {
+        const result = compileSQL({
+          where: func(`gte`, [ref(`quantity`), val(10)]),
+        })
+        expect(result.where).toBe(`"quantity" >= $1`)
+        expect(result.params).toEqual({ '1': `10` })
+      })
+
+      it(`should compile lte operator`, () => {
+        const result = compileSQL({
+          where: func(`lte`, [ref(`rating`), val(5)]),
+        })
+        expect(result.where).toBe(`"rating" <= $1`)
+        expect(result.params).toEqual({ '1': `5` })
+      })
+    })
+
+    describe(`compound where clauses`, () => {
+      it(`should compile AND with two conditions`, () => {
+        const result = compileSQL({
+          where: func(`and`, [
+            func(`eq`, [ref(`projectId`), val(`uuid-123`)]),
+            func(`gt`, [ref(`name`), val(`cursor-value`)]),
+          ]),
+        })
+        // Note: 2-arg AND doesn't add parentheses around the operands
+        expect(result.where).toBe(`"projectId" = $1 AND "name" > $2`)
+        expect(result.params).toEqual({ '1': `uuid-123`, '2': `cursor-value` })
+      })
+
+      it(`should compile AND with more than two conditions`, () => {
+        const result = compileSQL({
+          where: func(`and`, [
+            func(`eq`, [ref(`a`), val(`1`)]),
+            func(`eq`, [ref(`b`), val(`2`)]),
+            func(`eq`, [ref(`c`), val(`3`)]),
+          ]),
+        })
+        // >2 args adds parentheses
+        expect(result.where).toBe(`("a" = $1) AND ("b" = $2) AND ("c" = $3)`)
+        expect(result.params).toEqual({ '1': `1`, '2': `2`, '3': `3` })
+      })
+
+      it(`should compile OR with two conditions`, () => {
+        const result = compileSQL({
+          where: func(`or`, [
+            func(`eq`, [ref(`status`), val(`active`)]),
+            func(`eq`, [ref(`status`), val(`pending`)]),
+          ]),
+        })
+        expect(result.where).toBe(`"status" = $1 OR "status" = $2`)
+        expect(result.params).toEqual({ '1': `active`, '2': `pending` })
+      })
+    })
+
+    describe(`null/undefined value handling`, () => {
+      it(`should throw error for eq(col, null)`, () => {
+        // Users should use isNull() instead of eq(col, null)
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [ref(`deletedAt`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for eq(col, undefined)`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [ref(`deletedAt`), val(undefined)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for eq(null, col) (reversed order)`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [val(null), ref(`name`)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for gt with null value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`gt`, [ref(`age`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'gt' operator`)
+      })
+
+      it(`should throw error for lt with undefined value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`lt`, [ref(`age`), val(undefined)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'lt' operator`)
+      })
+
+      it(`should throw error for gte with null value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`gte`, [ref(`price`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'gte' operator`)
+      })
+
+      it(`should throw error for lte with null value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`lte`, [ref(`rating`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'lte' operator`)
+      })
+
+      it(`should throw error for like with null value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`like`, [ref(`name`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'like' operator`)
+      })
+
+      it(`should throw error for ilike with null value`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`ilike`, [ref(`name`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'ilike' operator`)
+      })
+
+      it(`should throw error for eq(col, null) in AND clause`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`and`, [
+              func(`eq`, [ref(`projectId`), val(`uuid-123`)]),
+              func(`eq`, [ref(`deletedAt`), val(null)]),
+            ]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for eq(col, null) in mixed conditions`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`and`, [
+              func(`eq`, [ref(`status`), val(`active`)]),
+              func(`eq`, [ref(`archivedAt`), val(null)]),
+              func(`gt`, [ref(`createdAt`), val(`2024-01-01`)]),
+            ]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should not include params for null values in complex queries`, () => {
+        // This test simulates the bug scenario: a query with both valid params and null
+        // Before the fix, this would generate:
+        //   where: "projectId" = $1 AND "name" > $2
+        //   params: { "1": "uuid" } // missing $2!
+        // After the fix, gt(name, null) throws an error
+        expect(() =>
+          compileSQL({
+            where: func(`and`, [
+              func(`eq`, [ref(`projectId`), val(`uuid`)]),
+              func(`gt`, [ref(`name`), val(null)]),
+            ]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'gt' operator`)
+      })
+
+      it(`should throw error for eq(null, null)`, () => {
+        // Both args are null - this is nonsensical and would cause missing params
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [val(null), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for eq(null, literal)`, () => {
+        // Comparing null to a literal is nonsensical (always evaluates to UNKNOWN)
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [val(null), val(42)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+
+      it(`should throw error for eq(col, null) - use isNull(col) instead`, () => {
+        // eq(col, null) should throw an error
+        // Users should use isNull(col) which works correctly
+        expect(() =>
+          compileSQL({
+            where: func(`eq`, [ref(`email`), val(null)]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+
+        // isNull(col) should work correctly
+        const isNullResult = compileSQL({
+          where: func(`isNull`, [ref(`email`)]),
+        })
+        expect(isNullResult.where).toBe(`"email" IS NULL`)
+        expect(isNullResult.params).toEqual({})
+      })
+
+      it(`should throw error for eq(col, null) in OR clause`, () => {
+        expect(() =>
+          compileSQL({
+            where: func(`or`, [
+              func(`eq`, [ref(`deletedAt`), val(null)]),
+              func(`eq`, [ref(`status`), val(`active`)]),
+            ]),
+          }),
+        ).toThrow(`Cannot use null/undefined value with 'eq' operator`)
+      })
+    })
+
+    describe(`isNull/isUndefined operators`, () => {
+      it(`should compile isNull correctly`, () => {
+        const result = compileSQL({
+          where: func(`isNull`, [ref(`deletedAt`)]),
+        })
+        expect(result.where).toBe(`"deletedAt" IS NULL`)
+        expect(result.params).toEqual({})
+      })
+
+      it(`should compile isUndefined correctly`, () => {
+        const result = compileSQL({
+          where: func(`isUndefined`, [ref(`field`)]),
+        })
+        expect(result.where).toBe(`"field" IS NULL`)
+        expect(result.params).toEqual({})
+      })
+
+      it(`should compile NOT isNull correctly`, () => {
+        const result = compileSQL({
+          where: func(`not`, [func(`isNull`, [ref(`name`)])]),
+        })
+        expect(result.where).toBe(`"name" IS NOT NULL`)
+        expect(result.params).toEqual({})
+      })
+    })
+
+    describe(`empty where clause`, () => {
+      it(`should add true = true when no where clause`, () => {
+        const result = compileSQL({})
+        expect(result.where).toBe(`true = true`)
+        expect(result.params).toEqual({})
+      })
+    })
+
+    describe(`limit`, () => {
+      it(`should include limit in result`, () => {
+        const result = compileSQL({ limit: 10 })
+        expect(result.limit).toBe(10)
+      })
+    })
+  })
+})