Extensive research measuring event-related brain potentials (ERPs) shows that semantic incongruity is indexed by the N400 effect and syntactic/structural incongruity is indexed by the P600 effect. We used these indices to examine how people coordinate their semantic and arithmetic knowledge when they read simple addition and division word problem sentences (e.g., Twelve roses plus three daisies equals fifteen). Prior work in problem solving has shown that word-problem solutions are modulated by analogical alignment of semantic and arithmetic relations, such that people avoid or commit errors on misaligned problems (e.g., Aligned: Twelve roses plus three daisies equals fifteen; Misaligned: Twelve cookies plus three jars equals fifteen). Here, we found that such analogical alignments modulate the comprehension of word-problem sentences. Specifically, we found that analogically Misaligned semantic relations elicited a P600 effect. Furthermore, an N400 effect was elicited by the last number word of Misaligned problem sentences, even when it was a mathematically correct answer. These results show that analogical alignment between semantic and arithmetic relations can be indexed with the P600 effect and provide a foundation for future ERP work on analogical reasoning.